1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 The tip tree handbook 3 The tip tree handbook
4 ===================== 4 =====================
5 5
6 What is the tip tree? 6 What is the tip tree?
7 --------------------- 7 ---------------------
8 8
9 The tip tree is a collection of several subsys 9 The tip tree is a collection of several subsystems and areas of
10 development. The tip tree is both a direct dev 10 development. The tip tree is both a direct development tree and a
11 aggregation tree for several sub-maintainer tr 11 aggregation tree for several sub-maintainer trees. The tip tree gitweb URL
12 is: https://git.kernel.org/pub/scm/linux/kerne 12 is: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
13 13
14 The tip tree contains the following subsystems 14 The tip tree contains the following subsystems:
15 15
16 - **x86 architecture** 16 - **x86 architecture**
17 17
18 The x86 architecture development takes pl 18 The x86 architecture development takes place in the tip tree except
19 for the x86 KVM and XEN specific parts wh 19 for the x86 KVM and XEN specific parts which are maintained in the
20 corresponding subsystems and routed direc 20 corresponding subsystems and routed directly to mainline from
21 there. It's still good practice to Cc the 21 there. It's still good practice to Cc the x86 maintainers on
22 x86-specific KVM and XEN patches. 22 x86-specific KVM and XEN patches.
23 23
24 Some x86 subsystems have their own mainta 24 Some x86 subsystems have their own maintainers in addition to the
25 overall x86 maintainers. Please Cc the o 25 overall x86 maintainers. Please Cc the overall x86 maintainers on
26 patches touching files in arch/x86 even w 26 patches touching files in arch/x86 even when they are not called out
27 by the MAINTAINER file. 27 by the MAINTAINER file.
28 28
29 Note, that ``x86@kernel.org`` is not a ma 29 Note, that ``x86@kernel.org`` is not a mailing list. It is merely a
30 mail alias which distributes mails to the 30 mail alias which distributes mails to the x86 top-level maintainer
31 team. Please always Cc the Linux Kernel m 31 team. Please always Cc the Linux Kernel mailing list (LKML)
32 ``linux-kernel@vger.kernel.org``, otherwi 32 ``linux-kernel@vger.kernel.org``, otherwise your mail ends up only in
33 the private inboxes of the maintainers. 33 the private inboxes of the maintainers.
34 34
35 - **Scheduler** 35 - **Scheduler**
36 36
37 Scheduler development takes place in the 37 Scheduler development takes place in the -tip tree, in the
38 sched/core branch - with occasional sub-t 38 sched/core branch - with occasional sub-topic trees for
39 work-in-progress patch-sets. 39 work-in-progress patch-sets.
40 40
41 - **Locking and atomics** 41 - **Locking and atomics**
42 42
43 Locking development (including atomics an 43 Locking development (including atomics and other synchronization
44 primitives that are connected to locking) 44 primitives that are connected to locking) takes place in the -tip
45 tree, in the locking/core branch - with o 45 tree, in the locking/core branch - with occasional sub-topic trees
46 for work-in-progress patch-sets. 46 for work-in-progress patch-sets.
47 47
48 - **Generic interrupt subsystem and interru 48 - **Generic interrupt subsystem and interrupt chip drivers**:
49 49
50 - interrupt core development happens in t 50 - interrupt core development happens in the irq/core branch
51 51
52 - interrupt chip driver development also 52 - interrupt chip driver development also happens in the irq/core
53 branch, but the patches are usually app 53 branch, but the patches are usually applied in a separate maintainer
54 tree and then aggregated into irq/core 54 tree and then aggregated into irq/core
55 55
56 - **Time, timers, timekeeping, NOHZ and rel 56 - **Time, timers, timekeeping, NOHZ and related chip drivers**:
57 57
58 - timekeeping, clocksource core, NTP and 58 - timekeeping, clocksource core, NTP and alarmtimer development
59 happens in the timers/core branch, but 59 happens in the timers/core branch, but patches are usually applied in
60 a separate maintainer tree and then agg 60 a separate maintainer tree and then aggregated into timers/core
61 61
62 - clocksource/event driver development ha 62 - clocksource/event driver development happens in the timers/core
63 branch, but patches are mostly applied 63 branch, but patches are mostly applied in a separate maintainer tree
64 and then aggregated into timers/core 64 and then aggregated into timers/core
65 65
66 - **Performance counters core, architecture 66 - **Performance counters core, architecture support and tooling**:
67 67
68 - perf core and architecture support deve 68 - perf core and architecture support development happens in the
69 perf/core branch 69 perf/core branch
70 70
71 - perf tooling development happens in the 71 - perf tooling development happens in the perf tools maintainer
72 tree and is aggregated into the tip tre 72 tree and is aggregated into the tip tree.
73 73
74 - **CPU hotplug core** 74 - **CPU hotplug core**
75 75
76 - **RAS core** 76 - **RAS core**
77 77
78 Mostly x86-specific RAS patches are colle 78 Mostly x86-specific RAS patches are collected in the tip ras/core
79 branch. 79 branch.
80 80
81 - **EFI core** 81 - **EFI core**
82 82
83 EFI development in the efi git tree. The 83 EFI development in the efi git tree. The collected patches are
84 aggregated in the tip efi/core branch. 84 aggregated in the tip efi/core branch.
85 85
86 - **RCU** 86 - **RCU**
87 87
88 RCU development happens in the linux-rcu 88 RCU development happens in the linux-rcu tree. The resulting changes
89 are aggregated into the tip core/rcu bran 89 are aggregated into the tip core/rcu branch.
90 90
91 - **Various core code components**: 91 - **Various core code components**:
92 92
93 - debugobjects 93 - debugobjects
94 94
95 - objtool 95 - objtool
96 96
97 - random bits and pieces 97 - random bits and pieces
98 98
99 99
100 Patch submission notes 100 Patch submission notes
101 ---------------------- 101 ----------------------
102 102
103 Selecting the tree/branch 103 Selecting the tree/branch
104 ^^^^^^^^^^^^^^^^^^^^^^^^^ 104 ^^^^^^^^^^^^^^^^^^^^^^^^^
105 105
106 In general, development against the head of th 106 In general, development against the head of the tip tree master branch is
107 fine, but for the subsystems which are maintai 107 fine, but for the subsystems which are maintained separately, have their
108 own git tree and are only aggregated into the 108 own git tree and are only aggregated into the tip tree, development should
109 take place against the relevant subsystem tree 109 take place against the relevant subsystem tree or branch.
110 110
111 Bug fixes which target mainline should always 111 Bug fixes which target mainline should always be applicable against the
112 mainline kernel tree. Potential conflicts agai 112 mainline kernel tree. Potential conflicts against changes which are already
113 queued in the tip tree are handled by the main 113 queued in the tip tree are handled by the maintainers.
114 114
115 Patch subject 115 Patch subject
116 ^^^^^^^^^^^^^ 116 ^^^^^^^^^^^^^
117 117
118 The tip tree preferred format for patch subjec 118 The tip tree preferred format for patch subject prefixes is
119 'subsys/component:', e.g. 'x86/apic:', 'x86/mm 119 'subsys/component:', e.g. 'x86/apic:', 'x86/mm/fault:', 'sched/fair:',
120 'genirq/core:'. Please do not use file names o 120 'genirq/core:'. Please do not use file names or complete file paths as
121 prefix. 'git log path/to/file' should give you 121 prefix. 'git log path/to/file' should give you a reasonable hint in most
122 cases. 122 cases.
123 123
124 The condensed patch description in the subject 124 The condensed patch description in the subject line should start with a
125 uppercase letter and should be written in impe 125 uppercase letter and should be written in imperative tone.
126 126
127 127
128 Changelog 128 Changelog
129 ^^^^^^^^^ 129 ^^^^^^^^^
130 130
131 The general rules about changelogs in the :ref !! 131 The general rules about changelogs in the process documentation, see
132 <describe_changes>`, apply. !! 132 :ref:`Documentation/process/ <submittingpatches>`, apply.
133 133
134 The tip tree maintainers set value on followin 134 The tip tree maintainers set value on following these rules, especially on
135 the request to write changelogs in imperative 135 the request to write changelogs in imperative mood and not impersonating
136 code or the execution of it. This is not just 136 code or the execution of it. This is not just a whim of the
137 maintainers. Changelogs written in abstract wo 137 maintainers. Changelogs written in abstract words are more precise and
138 tend to be less confusing than those written i 138 tend to be less confusing than those written in the form of novels.
139 139
140 It's also useful to structure the changelog in 140 It's also useful to structure the changelog into several paragraphs and not
141 lump everything together into a single one. A 141 lump everything together into a single one. A good structure is to explain
142 the context, the problem and the solution in s 142 the context, the problem and the solution in separate paragraphs and this
143 order. 143 order.
144 144
145 Examples for illustration: 145 Examples for illustration:
146 146
147 Example 1:: 147 Example 1::
148 148
149 x86/intel_rdt/mbm: Fix MBM overflow handle 149 x86/intel_rdt/mbm: Fix MBM overflow handler during hot cpu
150 150
151 When a CPU is dying, we cancel the worker 151 When a CPU is dying, we cancel the worker and schedule a new worker on a
152 different CPU on the same domain. But if t 152 different CPU on the same domain. But if the timer is already about to
153 expire (say 0.99s) then we essentially dou 153 expire (say 0.99s) then we essentially double the interval.
154 154
155 We modify the hot cpu handling to cancel t 155 We modify the hot cpu handling to cancel the delayed work on the dying
156 cpu and run the worker immediately on a di 156 cpu and run the worker immediately on a different cpu in same domain. We
157 do not flush the worker because the MBM ov !! 157 donot flush the worker because the MBM overflow worker reschedules the
158 worker on same CPU and scans the domain->c 158 worker on same CPU and scans the domain->cpu_mask to get the domain
159 pointer. 159 pointer.
160 160
161 Improved version:: 161 Improved version::
162 162
163 x86/intel_rdt/mbm: Fix MBM overflow handle 163 x86/intel_rdt/mbm: Fix MBM overflow handler during CPU hotplug
164 164
165 When a CPU is dying, the overflow worker i 165 When a CPU is dying, the overflow worker is canceled and rescheduled on a
166 different CPU in the same domain. But if t 166 different CPU in the same domain. But if the timer is already about to
167 expire this essentially doubles the interv 167 expire this essentially doubles the interval which might result in a non
168 detected overflow. 168 detected overflow.
169 169
170 Cancel the overflow worker and reschedule 170 Cancel the overflow worker and reschedule it immediately on a different CPU
171 in the same domain. The work could be flus 171 in the same domain. The work could be flushed as well, but that would
172 reschedule it on the same CPU. 172 reschedule it on the same CPU.
173 173
174 Example 2:: 174 Example 2::
175 175
176 time: POSIX CPU timers: Ensure that variab 176 time: POSIX CPU timers: Ensure that variable is initialized
177 177
178 If cpu_timer_sample_group returns -EINVAL, 178 If cpu_timer_sample_group returns -EINVAL, it will not have written into
179 *sample. Checking for cpu_timer_sample_gro 179 *sample. Checking for cpu_timer_sample_group's return value precludes the
180 potential use of an uninitialized value of 180 potential use of an uninitialized value of now in the following block.
181 Given an invalid clock_idx, the previous c 181 Given an invalid clock_idx, the previous code could otherwise overwrite
182 *oldval in an undefined manner. This is no 182 *oldval in an undefined manner. This is now prevented. We also exploit
183 short-circuiting of && to sample the timer 183 short-circuiting of && to sample the timer only if the result will
184 actually be used to update *oldval. 184 actually be used to update *oldval.
185 185
186 Improved version:: 186 Improved version::
187 187
188 posix-cpu-timers: Make set_process_cpu_tim 188 posix-cpu-timers: Make set_process_cpu_timer() more robust
189 189
190 Because the return value of cpu_timer_samp 190 Because the return value of cpu_timer_sample_group() is not checked,
191 compilers and static checkers can legitima 191 compilers and static checkers can legitimately warn about a potential use
192 of the uninitialized variable 'now'. This 192 of the uninitialized variable 'now'. This is not a runtime issue as all
193 call sites hand in valid clock ids. 193 call sites hand in valid clock ids.
194 194
195 Also cpu_timer_sample_group() is invoked u 195 Also cpu_timer_sample_group() is invoked unconditionally even when the
196 result is not used because *oldval is NULL 196 result is not used because *oldval is NULL.
197 197
198 Make the invocation conditional and check 198 Make the invocation conditional and check the return value.
199 199
200 Example 3:: 200 Example 3::
201 201
202 The entity can also be used for other purp 202 The entity can also be used for other purposes.
203 203
204 Let's rename it to be more generic. 204 Let's rename it to be more generic.
205 205
206 Improved version:: 206 Improved version::
207 207
208 The entity can also be used for other purp 208 The entity can also be used for other purposes.
209 209
210 Rename it to be more generic. 210 Rename it to be more generic.
211 211
212 212
213 For complex scenarios, especially race conditi 213 For complex scenarios, especially race conditions and memory ordering
214 issues, it is valuable to depict the scenario 214 issues, it is valuable to depict the scenario with a table which shows
215 the parallelism and the temporal order of even 215 the parallelism and the temporal order of events. Here is an example::
216 216
217 CPU0 CPU1 217 CPU0 CPU1
218 free_irq(X) interrupt 218 free_irq(X) interrupt X
219 spin_lock( 219 spin_lock(desc->lock)
220 wake irq t 220 wake irq thread()
221 spin_unloc 221 spin_unlock(desc->lock)
222 spin_lock(desc->lock) 222 spin_lock(desc->lock)
223 remove action() 223 remove action()
224 shutdown_irq() 224 shutdown_irq()
225 release_resources() thread_han 225 release_resources() thread_handler()
226 spin_unlock(desc->lock) access r 226 spin_unlock(desc->lock) access released resources.
227 ^^^^^^^^ 227 ^^^^^^^^^^^^^^^^^^^^^^^^^
228 synchronize_irq() 228 synchronize_irq()
229 229
230 Lockdep provides similar useful output to depi 230 Lockdep provides similar useful output to depict a possible deadlock
231 scenario:: 231 scenario::
232 232
233 CPU0 CP 233 CPU0 CPU1
234 rtmutex_lock(&rcu->rt_mutex) 234 rtmutex_lock(&rcu->rt_mutex)
235 spin_lock(&rcu->rt_mutex.wait_lock) 235 spin_lock(&rcu->rt_mutex.wait_lock)
236 lo 236 local_irq_disable()
237 sp 237 spin_lock(&timer->it_lock)
238 sp 238 spin_lock(&rcu->mutex.wait_lock)
239 --> Interrupt 239 --> Interrupt
240 spin_lock(&timer->it_lock) 240 spin_lock(&timer->it_lock)
241 241
242 242
243 Function references in changelogs 243 Function references in changelogs
244 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 244 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
245 245
246 When a function is mentioned in the changelog, 246 When a function is mentioned in the changelog, either the text body or the
247 subject line, please use the format 'function_ 247 subject line, please use the format 'function_name()'. Omitting the
248 brackets after the function name can be ambigu 248 brackets after the function name can be ambiguous::
249 249
250 Subject: subsys/component: Make reservation_ 250 Subject: subsys/component: Make reservation_count static
251 251
252 reservation_count is only used in reservatio 252 reservation_count is only used in reservation_stats. Make it static.
253 253
254 The variant with brackets is more precise:: 254 The variant with brackets is more precise::
255 255
256 Subject: subsys/component: Make reservation_ 256 Subject: subsys/component: Make reservation_count() static
257 257
258 reservation_count() is only called from rese 258 reservation_count() is only called from reservation_stats(). Make it
259 static. 259 static.
260 260
261 261
262 Backtraces in changelogs 262 Backtraces in changelogs
263 ^^^^^^^^^^^^^^^^^^^^^^^^ 263 ^^^^^^^^^^^^^^^^^^^^^^^^
264 264
265 See :ref:`backtraces`. 265 See :ref:`backtraces`.
266 266
267 Ordering of commit tags 267 Ordering of commit tags
268 ^^^^^^^^^^^^^^^^^^^^^^^ 268 ^^^^^^^^^^^^^^^^^^^^^^^
269 269
270 To have a uniform view of the commit tags, the 270 To have a uniform view of the commit tags, the tip maintainers use the
271 following tag ordering scheme: 271 following tag ordering scheme:
272 272
273 - Fixes: 12char-SHA1 ("sub/sys: Original subj 273 - Fixes: 12char-SHA1 ("sub/sys: Original subject line")
274 274
275 A Fixes tag should be added even for change 275 A Fixes tag should be added even for changes which do not need to be
276 backported to stable kernels, i.e. when add 276 backported to stable kernels, i.e. when addressing a recently introduced
277 issue which only affects tip or the current 277 issue which only affects tip or the current head of mainline. These tags
278 are helpful to identify the original commit 278 are helpful to identify the original commit and are much more valuable
279 than prominently mentioning the commit whic 279 than prominently mentioning the commit which introduced a problem in the
280 text of the changelog itself because they c 280 text of the changelog itself because they can be automatically
281 extracted. 281 extracted.
282 282
283 The following example illustrates the diffe 283 The following example illustrates the difference::
284 284
285 Commit 285 Commit
286 286
287 abcdef012345678 ("x86/xxx: Replace foo 287 abcdef012345678 ("x86/xxx: Replace foo with bar")
288 288
289 left an unused instance of variable foo a 289 left an unused instance of variable foo around. Remove it.
290 290
291 Signed-off-by: J.Dev <j.dev@mail> 291 Signed-off-by: J.Dev <j.dev@mail>
292 292
293 Please say instead:: 293 Please say instead::
294 294
295 The recent replacement of foo with bar le 295 The recent replacement of foo with bar left an unused instance of
296 variable foo around. Remove it. 296 variable foo around. Remove it.
297 297
298 Fixes: abcdef012345678 ("x86/xxx: Replace 298 Fixes: abcdef012345678 ("x86/xxx: Replace foo with bar")
299 Signed-off-by: J.Dev <j.dev@mail> 299 Signed-off-by: J.Dev <j.dev@mail>
300 300
301 The latter puts the information about the p 301 The latter puts the information about the patch into the focus and
302 amends it with the reference to the commit 302 amends it with the reference to the commit which introduced the issue
303 rather than putting the focus on the origin 303 rather than putting the focus on the original commit in the first place.
304 304
305 - Reported-by: ``Reporter <reporter@mail>`` 305 - Reported-by: ``Reporter <reporter@mail>``
306 306
307 - Closes: ``URL or Message-ID of the bug repo <<
308 <<
309 - Originally-by: ``Original author <original-a 307 - Originally-by: ``Original author <original-author@mail>``
310 308
311 - Suggested-by: ``Suggester <suggester@mail>`` 309 - Suggested-by: ``Suggester <suggester@mail>``
312 310
313 - Co-developed-by: ``Co-author <co-author@mail 311 - Co-developed-by: ``Co-author <co-author@mail>``
314 312
315 Signed-off-by: ``Co-author <co-author@mail>` !! 313 Signed-off: ``Co-author <co-author@mail>``
316 314
317 Note, that Co-developed-by and Signed-off-b 315 Note, that Co-developed-by and Signed-off-by of the co-author(s) must
318 come in pairs. 316 come in pairs.
319 317
320 - Signed-off-by: ``Author <author@mail>`` 318 - Signed-off-by: ``Author <author@mail>``
321 319
322 The first Signed-off-by (SOB) after the las 320 The first Signed-off-by (SOB) after the last Co-developed-by/SOB pair is the
323 author SOB, i.e. the person flagged as auth 321 author SOB, i.e. the person flagged as author by git.
324 322
325 - Signed-off-by: ``Patch handler <handler@mail 323 - Signed-off-by: ``Patch handler <handler@mail>``
326 324
327 SOBs after the author SOB are from people h 325 SOBs after the author SOB are from people handling and transporting
328 the patch, but were not involved in develop 326 the patch, but were not involved in development. SOB chains should
329 reflect the **real** route a patch took as 327 reflect the **real** route a patch took as it was propagated to us,
330 with the first SOB entry signalling primary 328 with the first SOB entry signalling primary authorship of a single
331 author. Acks should be given as Acked-by li 329 author. Acks should be given as Acked-by lines and review approvals
332 as Reviewed-by lines. 330 as Reviewed-by lines.
333 331
334 If the handler made modifications to the pa 332 If the handler made modifications to the patch or the changelog, then
335 this should be mentioned **after** the chan 333 this should be mentioned **after** the changelog text and **above**
336 all commit tags in the following format:: 334 all commit tags in the following format::
337 335
338 ... changelog text ends. 336 ... changelog text ends.
339 337
340 [ handler: Replaced foo by bar and update 338 [ handler: Replaced foo by bar and updated changelog ]
341 339
342 First-tag: ..... 340 First-tag: .....
343 341
344 Note the two empty new lines which separate 342 Note the two empty new lines which separate the changelog text and the
345 commit tags from that notice. 343 commit tags from that notice.
346 344
347 If a patch is sent to the mailing list by a 345 If a patch is sent to the mailing list by a handler then the author has
348 to be noted in the first line of the change 346 to be noted in the first line of the changelog with::
349 347
350 From: Author <author@mail> 348 From: Author <author@mail>
351 349
352 Changelog text starts here.... 350 Changelog text starts here....
353 351
354 so the authorship is preserved. The 'From:' 352 so the authorship is preserved. The 'From:' line has to be followed
355 by a empty newline. If that 'From:' line is 353 by a empty newline. If that 'From:' line is missing, then the patch
356 would be attributed to the person who sent 354 would be attributed to the person who sent (transported, handled) it.
357 The 'From:' line is automatically removed w 355 The 'From:' line is automatically removed when the patch is applied
358 and does not show up in the final git chang 356 and does not show up in the final git changelog. It merely affects
359 the authorship information of the resulting 357 the authorship information of the resulting Git commit.
360 358
361 - Tested-by: ``Tester <tester@mail>`` 359 - Tested-by: ``Tester <tester@mail>``
362 360
363 - Reviewed-by: ``Reviewer <reviewer@mail>`` 361 - Reviewed-by: ``Reviewer <reviewer@mail>``
364 362
365 - Acked-by: ``Acker <acker@mail>`` 363 - Acked-by: ``Acker <acker@mail>``
366 364
367 - Cc: ``cc-ed-person <person@mail>`` 365 - Cc: ``cc-ed-person <person@mail>``
368 366
369 If the patch should be backported to stable 367 If the patch should be backported to stable, then please add a '``Cc:
370 stable@vger.kernel.org``' tag, but do not C 368 stable@vger.kernel.org``' tag, but do not Cc stable when sending your
371 mail. 369 mail.
372 370
373 - Link: ``https://link/to/information`` 371 - Link: ``https://link/to/information``
374 372
375 For referring to an email posted to the ker !! 373 For referring to an email on LKML or other kernel mailing lists,
376 use the lore.kernel.org redirector URL:: !! 374 please use the lore.kernel.org redirector URL::
377 375
378 Link: https://lore.kernel.org/email-messa !! 376 https://lore.kernel.org/r/email-message@id
379 377
380 This URL should be used when referring to r !! 378 The kernel.org redirector is considered a stable URL, unlike other email
381 topics, related patch sets, or other notabl !! 379 archives.
382 A convenient way to associate ``Link:`` tra <<
383 message is to use markdown-like bracketed n <<
384 <<
385 A similar approach was attempted before a <<
386 effort [1], but the initial implementatio <<
387 regressions [2], so it was backed out and <<
388 <<
389 Link: https://lore.kernel.org/some-msgid@ <<
390 Link: https://bugzilla.example.org/bug/12 <<
391 <<
392 You can also use ``Link:`` trailers to indi <<
393 patch when applying it to your git tree. In <<
394 dedicated ``patch.msgid.link`` domain inste <<
395 This practice makes it possible for automat <<
396 which link to use to retrieve the original <<
397 example:: <<
398 380
399 Link: https://patch.msgid.link/patch-sour !! 381 Maintainers will add a Link tag referencing the email of the patch
>> 382 submission when they apply a patch to the tip tree. This tag is useful
>> 383 for later reference and is also used for commit notifications.
400 384
401 Please do not use combined tags, e.g. ``Report 385 Please do not use combined tags, e.g. ``Reported-and-tested-by``, as
402 they just complicate automated extraction of t 386 they just complicate automated extraction of tags.
403 387
404 388
405 Links to documentation 389 Links to documentation
406 ^^^^^^^^^^^^^^^^^^^^^^ 390 ^^^^^^^^^^^^^^^^^^^^^^
407 391
408 Providing links to documentation in the change 392 Providing links to documentation in the changelog is a great help to later
409 debugging and analysis. Unfortunately, URLs o 393 debugging and analysis. Unfortunately, URLs often break very quickly
410 because companies restructure their websites f 394 because companies restructure their websites frequently. Non-'volatile'
411 exceptions include the Intel SDM and the AMD A 395 exceptions include the Intel SDM and the AMD APM.
412 396
413 Therefore, for 'volatile' documents, please cr 397 Therefore, for 'volatile' documents, please create an entry in the kernel
414 bugzilla https://bugzilla.kernel.org and attac 398 bugzilla https://bugzilla.kernel.org and attach a copy of these documents
415 to the bugzilla entry. Finally, provide the UR 399 to the bugzilla entry. Finally, provide the URL of the bugzilla entry in
416 the changelog. 400 the changelog.
417 401
418 Patch resend or reminders 402 Patch resend or reminders
419 ^^^^^^^^^^^^^^^^^^^^^^^^^ 403 ^^^^^^^^^^^^^^^^^^^^^^^^^
420 404
421 See :ref:`resend_reminders`. 405 See :ref:`resend_reminders`.
422 406
423 Merge window 407 Merge window
424 ^^^^^^^^^^^^ 408 ^^^^^^^^^^^^
425 409
426 Please do not expect patches to be reviewed or !! 410 Please do not expect large patch series to be handled during the merge
427 maintainers around or during the merge window. !! 411 window or even during the week before. Such patches should be submitted in
428 to all but urgent fixes during this time. The !! 412 mergeable state *at* *least* a week before the merge window opens.
429 window closes and a new -rc1 kernel has been r !! 413 Exceptions are made for bug fixes and *sometimes* for small standalone
430 !! 414 drivers for new hardware or minimally invasive patches for hardware
431 Large series should be submitted in mergeable !! 415 enablement.
432 before the merge window opens. Exceptions are <<
433 *sometimes* for small standalone drivers for n <<
434 invasive patches for hardware enablement. <<
435 416
436 During the merge window, the maintainers inste 417 During the merge window, the maintainers instead focus on following the
437 upstream changes, fixing merge window fallout, 418 upstream changes, fixing merge window fallout, collecting bug fixes, and
438 allowing themselves a breath. Please respect t 419 allowing themselves a breath. Please respect that.
439 420
440 So called _urgent_ branches will be merged int !! 421 The release candidate -rc1 is the starting point for new patches to be
441 stabilization phase of each release. !! 422 applied which are targeted for the next merge window.
442 423
443 424
444 Git 425 Git
445 ^^^ 426 ^^^
446 427
447 The tip maintainers accept git pull requests f 428 The tip maintainers accept git pull requests from maintainers who provide
448 subsystem changes for aggregation in the tip t 429 subsystem changes for aggregation in the tip tree.
449 430
450 Pull requests for new patch submissions are us 431 Pull requests for new patch submissions are usually not accepted and do not
451 replace proper patch submission to the mailing 432 replace proper patch submission to the mailing list. The main reason for
452 this is that the review workflow is email base 433 this is that the review workflow is email based.
453 434
454 If you submit a larger patch series it is help 435 If you submit a larger patch series it is helpful to provide a git branch
455 in a private repository which allows intereste 436 in a private repository which allows interested people to easily pull the
456 series for testing. The usual way to offer thi 437 series for testing. The usual way to offer this is a git URL in the cover
457 letter of the patch series. 438 letter of the patch series.
458 439
459 Testing <<
460 ^^^^^^^ <<
461 <<
462 Code should be tested before submitting to the <<
463 other than minor changes should be built, boot <<
464 comprehensive (and heavyweight) kernel debuggi <<
465 <<
466 These debugging options can be found in kernel <<
467 and can be added to an existing kernel config <<
468 <<
469 make x86_debug.config <<
470 <<
471 Some of these options are x86-specific and can <<
472 on other architectures. <<
473 <<
474 .. _maintainer-tip-coding-style: <<
475 440
476 Coding style notes 441 Coding style notes
477 ------------------ 442 ------------------
478 443
479 Comment style 444 Comment style
480 ^^^^^^^^^^^^^ 445 ^^^^^^^^^^^^^
481 446
482 Sentences in comments start with an uppercase 447 Sentences in comments start with an uppercase letter.
483 448
484 Single line comments:: 449 Single line comments::
485 450
486 /* This is a single line comment */ 451 /* This is a single line comment */
487 452
488 Multi-line comments:: 453 Multi-line comments::
489 454
490 /* 455 /*
491 * This is a properly formatted 456 * This is a properly formatted
492 * multi-line comment. 457 * multi-line comment.
493 * 458 *
494 * Larger multi-line comments should b 459 * Larger multi-line comments should be split into paragraphs.
495 */ 460 */
496 461
497 No tail comments (see below): !! 462 No tail comments:
498 463
499 Please refrain from using tail comments. Tai 464 Please refrain from using tail comments. Tail comments disturb the
500 reading flow in almost all contexts, but esp 465 reading flow in almost all contexts, but especially in code::
501 466
502 if (somecondition_is_true) /* Don't pu 467 if (somecondition_is_true) /* Don't put a comment here */
503 dostuff(); /* Neither here */ 468 dostuff(); /* Neither here */
504 469
505 seed = MAGIC_CONSTANT; /* Nor here */ 470 seed = MAGIC_CONSTANT; /* Nor here */
506 471
507 Use freestanding comments instead:: 472 Use freestanding comments instead::
508 473
509 /* This condition is not obvious witho 474 /* This condition is not obvious without a comment */
510 if (somecondition_is_true) { 475 if (somecondition_is_true) {
511 /* This really needs to be doc 476 /* This really needs to be documented */
512 dostuff(); 477 dostuff();
513 } 478 }
514 479
515 /* This magic initialization needs a c 480 /* This magic initialization needs a comment. Maybe not? */
516 seed = MAGIC_CONSTANT; 481 seed = MAGIC_CONSTANT;
517 <<
518 Use C++ style, tail comments when documentin <<
519 achieve a more compact layout and better rea <<
520 <<
521 // eax <<
522 u32 x2apic_shift : 5, // Numbe <<
523 // for t <<
524 : 27; // Reser <<
525 // ebx <<
526 u32 num_processors : 16, // Numbe <<
527 : 16; // Reser <<
528 <<
529 versus:: <<
530 <<
531 /* eax */ <<
532 /* <<
533 * Number of bits to shift API <<
534 * at the next level <<
535 */ <<
536 u32 x2apic_shift : 5, <<
537 /* Reserved */ <<
538 : 27; <<
539 <<
540 /* ebx */ <<
541 /* Number of processors at cur <<
542 u32 num_processors : 16, <<
543 /* Reserved */ <<
544 : 16; <<
545 482
546 Comment the important things: 483 Comment the important things:
547 484
548 Comments should be added where the operation 485 Comments should be added where the operation is not obvious. Documenting
549 the obvious is just a distraction:: 486 the obvious is just a distraction::
550 487
551 /* Decrement refcount and check for ze 488 /* Decrement refcount and check for zero */
552 if (refcount_dec_and_test(&p->refcnt)) 489 if (refcount_dec_and_test(&p->refcnt)) {
553 do; 490 do;
554 lots; 491 lots;
555 of; 492 of;
556 magic; 493 magic;
557 things; 494 things;
558 } 495 }
559 496
560 Instead, comments should explain the non-obv 497 Instead, comments should explain the non-obvious details and document
561 constraints:: 498 constraints::
562 499
563 if (refcount_dec_and_test(&p->refcnt)) 500 if (refcount_dec_and_test(&p->refcnt)) {
564 /* 501 /*
565 * Really good explanation why 502 * Really good explanation why the magic things below
566 * need to be done, ordering a 503 * need to be done, ordering and locking constraints,
567 * etc.. 504 * etc..
568 */ 505 */
569 do; 506 do;
570 lots; 507 lots;
571 of; 508 of;
572 magic; 509 magic;
573 /* Needs to be the last operat 510 /* Needs to be the last operation because ... */
574 things; 511 things;
575 } 512 }
576 513
577 Function documentation comments: 514 Function documentation comments:
578 515
579 To document functions and their arguments pl 516 To document functions and their arguments please use kernel-doc format
580 and not free form comments:: 517 and not free form comments::
581 518
582 /** 519 /**
583 * magic_function - Do lots of magic s 520 * magic_function - Do lots of magic stuff
584 * @magic: Pointer to the magic d 521 * @magic: Pointer to the magic data to operate on
585 * @offset: Offset in the data arr 522 * @offset: Offset in the data array of @magic
586 * 523 *
587 * Deep explanation of mysterious thin 524 * Deep explanation of mysterious things done with @magic along
588 * with documentation of the return va 525 * with documentation of the return values.
589 * 526 *
590 * Note, that the argument descriptors 527 * Note, that the argument descriptors above are arranged
591 * in a tabular fashion. 528 * in a tabular fashion.
592 */ 529 */
593 530
594 This applies especially to globally visible 531 This applies especially to globally visible functions and inline
595 functions in public header files. It might b 532 functions in public header files. It might be overkill to use kernel-doc
596 format for every (static) function which nee 533 format for every (static) function which needs a tiny explanation. The
597 usage of descriptive function names often re 534 usage of descriptive function names often replaces these tiny comments.
598 Apply common sense as always. 535 Apply common sense as always.
599 536
600 537
601 Documenting locking requirements 538 Documenting locking requirements
602 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 539 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
603 Documenting locking requirements is a good t 540 Documenting locking requirements is a good thing, but comments are not
604 necessarily the best choice. Instead of writ 541 necessarily the best choice. Instead of writing::
605 542
606 /* Caller must hold foo->lock */ 543 /* Caller must hold foo->lock */
607 void func(struct foo *foo) 544 void func(struct foo *foo)
608 { 545 {
609 ... 546 ...
610 } 547 }
611 548
612 Please use:: 549 Please use::
613 550
614 void func(struct foo *foo) 551 void func(struct foo *foo)
615 { 552 {
616 lockdep_assert_held(&foo->lock 553 lockdep_assert_held(&foo->lock);
617 ... 554 ...
618 } 555 }
619 556
620 In PROVE_LOCKING kernels, lockdep_assert_hel 557 In PROVE_LOCKING kernels, lockdep_assert_held() emits a warning
621 if the caller doesn't hold the lock. Commen 558 if the caller doesn't hold the lock. Comments can't do that.
622 559
623 Bracket rules 560 Bracket rules
624 ^^^^^^^^^^^^^ 561 ^^^^^^^^^^^^^
625 562
626 Brackets should be omitted only if the stateme 563 Brackets should be omitted only if the statement which follows 'if', 'for',
627 'while' etc. is truly a single line:: 564 'while' etc. is truly a single line::
628 565
629 if (foo) 566 if (foo)
630 do_something(); 567 do_something();
631 568
632 The following is not considered to be a single 569 The following is not considered to be a single line statement even
633 though C does not require brackets:: 570 though C does not require brackets::
634 571
635 for (i = 0; i < end; i++) 572 for (i = 0; i < end; i++)
636 if (foo[i]) 573 if (foo[i])
637 do_something(foo[i]); 574 do_something(foo[i]);
638 575
639 Adding brackets around the outer loop enhances 576 Adding brackets around the outer loop enhances the reading flow::
640 577
641 for (i = 0; i < end; i++) { 578 for (i = 0; i < end; i++) {
642 if (foo[i]) 579 if (foo[i])
643 do_something(foo[i]); 580 do_something(foo[i]);
644 } 581 }
645 582
646 583
647 Variable declarations 584 Variable declarations
648 ^^^^^^^^^^^^^^^^^^^^^ 585 ^^^^^^^^^^^^^^^^^^^^^
649 586
650 The preferred ordering of variable declaration 587 The preferred ordering of variable declarations at the beginning of a
651 function is reverse fir tree order:: 588 function is reverse fir tree order::
652 589
653 struct long_struct_name *descriptive_n 590 struct long_struct_name *descriptive_name;
654 unsigned long foo, bar; 591 unsigned long foo, bar;
655 unsigned int tmp; 592 unsigned int tmp;
656 int ret; 593 int ret;
657 594
658 The above is faster to parse than the reverse 595 The above is faster to parse than the reverse ordering::
659 596
660 int ret; 597 int ret;
661 unsigned int tmp; 598 unsigned int tmp;
662 unsigned long foo, bar; 599 unsigned long foo, bar;
663 struct long_struct_name *descriptive_n 600 struct long_struct_name *descriptive_name;
664 601
665 And even more so than random ordering:: 602 And even more so than random ordering::
666 603
667 unsigned long foo, bar; 604 unsigned long foo, bar;
668 int ret; 605 int ret;
669 struct long_struct_name *descriptive_n 606 struct long_struct_name *descriptive_name;
670 unsigned int tmp; 607 unsigned int tmp;
671 608
672 Also please try to aggregate variables of the 609 Also please try to aggregate variables of the same type into a single
673 line. There is no point in wasting screen spac 610 line. There is no point in wasting screen space::
674 611
675 unsigned long a; 612 unsigned long a;
676 unsigned long b; 613 unsigned long b;
677 unsigned long c; 614 unsigned long c;
678 unsigned long d; 615 unsigned long d;
679 616
680 It's really sufficient to do:: 617 It's really sufficient to do::
681 618
682 unsigned long a, b, c, d; 619 unsigned long a, b, c, d;
683 620
684 Please also refrain from introducing line spli 621 Please also refrain from introducing line splits in variable declarations::
685 622
686 struct long_struct_name *descriptive_n 623 struct long_struct_name *descriptive_name = container_of(bar,
687 624 struct long_struct_name,
688 625 member);
689 struct foobar foo; 626 struct foobar foo;
690 627
691 It's way better to move the initialization to 628 It's way better to move the initialization to a separate line after the
692 declarations:: 629 declarations::
693 630
694 struct long_struct_name *descriptive_n 631 struct long_struct_name *descriptive_name;
695 struct foobar foo; 632 struct foobar foo;
696 633
697 descriptive_name = container_of(bar, s 634 descriptive_name = container_of(bar, struct long_struct_name, member);
698 635
699 636
700 Variable types 637 Variable types
701 ^^^^^^^^^^^^^^ 638 ^^^^^^^^^^^^^^
702 639
703 Please use the proper u8, u16, u32, u64 types 640 Please use the proper u8, u16, u32, u64 types for variables which are meant
704 to describe hardware or are used as arguments 641 to describe hardware or are used as arguments for functions which access
705 hardware. These types are clearly defining the 642 hardware. These types are clearly defining the bit width and avoid
706 truncation, expansion and 32/64-bit confusion. 643 truncation, expansion and 32/64-bit confusion.
707 644
708 u64 is also recommended in code which would be 645 u64 is also recommended in code which would become ambiguous for 32-bit
709 kernels when 'unsigned long' would be used ins 646 kernels when 'unsigned long' would be used instead. While in such
710 situations 'unsigned long long' could be used 647 situations 'unsigned long long' could be used as well, u64 is shorter
711 and also clearly shows that the operation is r 648 and also clearly shows that the operation is required to be 64 bits wide
712 independent of the target CPU. 649 independent of the target CPU.
713 650
714 Please use 'unsigned int' instead of 'unsigned 651 Please use 'unsigned int' instead of 'unsigned'.
715 652
716 653
717 Constants 654 Constants
718 ^^^^^^^^^ 655 ^^^^^^^^^
719 656
720 Please do not use literal (hexa)decimal number 657 Please do not use literal (hexa)decimal numbers in code or initializers.
721 Either use proper defines which have descripti 658 Either use proper defines which have descriptive names or consider using
722 an enum. 659 an enum.
723 660
724 661
725 Struct declarations and initializers 662 Struct declarations and initializers
726 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 663 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
727 664
728 Struct declarations should align the struct me 665 Struct declarations should align the struct member names in a tabular
729 fashion:: 666 fashion::
730 667
731 struct bar_order { 668 struct bar_order {
732 unsigned int guest_id; 669 unsigned int guest_id;
733 int ordered_item; 670 int ordered_item;
734 struct menu *menu; 671 struct menu *menu;
735 }; 672 };
736 673
737 Please avoid documenting struct members within 674 Please avoid documenting struct members within the declaration, because
738 this often results in strangely formatted comm 675 this often results in strangely formatted comments and the struct members
739 become obfuscated:: 676 become obfuscated::
740 677
741 struct bar_order { 678 struct bar_order {
742 unsigned int guest_id; /* U 679 unsigned int guest_id; /* Unique guest id */
743 int ordered_item; 680 int ordered_item;
744 /* Pointer to a menu instance 681 /* Pointer to a menu instance which contains all the drinks */
745 struct menu *menu; 682 struct menu *menu;
746 }; 683 };
747 684
748 Instead, please consider using the kernel-doc 685 Instead, please consider using the kernel-doc format in a comment preceding
749 the struct declaration, which is easier to rea 686 the struct declaration, which is easier to read and has the added advantage
750 of including the information in the kernel doc 687 of including the information in the kernel documentation, for example, as
751 follows:: 688 follows::
752 689
753 690
754 /** 691 /**
755 * struct bar_order - Description of a 692 * struct bar_order - Description of a bar order
756 * @guest_id: Unique guest i 693 * @guest_id: Unique guest id
757 * @ordered_item: The item numbe 694 * @ordered_item: The item number from the menu
758 * @menu: Pointer to the 695 * @menu: Pointer to the menu from which the item
759 * was ordered 696 * was ordered
760 * 697 *
761 * Supplementary information for using 698 * Supplementary information for using the struct.
762 * 699 *
763 * Note, that the struct member descri 700 * Note, that the struct member descriptors above are arranged
764 * in a tabular fashion. 701 * in a tabular fashion.
765 */ 702 */
766 struct bar_order { 703 struct bar_order {
767 unsigned int guest_id; 704 unsigned int guest_id;
768 int ordered_item; 705 int ordered_item;
769 struct menu *menu; 706 struct menu *menu;
770 }; 707 };
771 708
772 Static struct initializers must use C99 initia 709 Static struct initializers must use C99 initializers and should also be
773 aligned in a tabular fashion:: 710 aligned in a tabular fashion::
774 711
775 static struct foo statfoo = { 712 static struct foo statfoo = {
776 .a = 0, 713 .a = 0,
777 .plain_integer = CONSTANT_DEF 714 .plain_integer = CONSTANT_DEFINE_OR_ENUM,
778 .bar = &statbar, 715 .bar = &statbar,
779 }; 716 };
780 717
781 Note that while C99 syntax allows the omission 718 Note that while C99 syntax allows the omission of the final comma,
782 we recommend the use of a comma on the last li 719 we recommend the use of a comma on the last line because it makes
783 reordering and addition of new lines easier, a 720 reordering and addition of new lines easier, and makes such future
784 patches slightly easier to read as well. 721 patches slightly easier to read as well.
785 722
786 Line breaks 723 Line breaks
787 ^^^^^^^^^^^ 724 ^^^^^^^^^^^
788 725
789 Restricting line length to 80 characters makes 726 Restricting line length to 80 characters makes deeply indented code hard to
790 read. Consider breaking out code into helper 727 read. Consider breaking out code into helper functions to avoid excessive
791 line breaking. 728 line breaking.
792 729
793 The 80 character rule is not a strict rule, so 730 The 80 character rule is not a strict rule, so please use common sense when
794 breaking lines. Especially format strings shou 731 breaking lines. Especially format strings should never be broken up.
795 732
796 When splitting function declarations or functi 733 When splitting function declarations or function calls, then please align
797 the first argument in the second line with the 734 the first argument in the second line with the first argument in the first
798 line:: 735 line::
799 736
800 static int long_function_name(struct foobar 737 static int long_function_name(struct foobar *barfoo, unsigned int id,
801 unsigned int o 738 unsigned int offset)
802 { 739 {
803 740
804 if (!id) { 741 if (!id) {
805 ret = longer_function_name(bar 742 ret = longer_function_name(barfoo, DEFAULT_BARFOO_ID,
806 off 743 offset);
807 ... 744 ...
808 745
809 Namespaces 746 Namespaces
810 ^^^^^^^^^^ 747 ^^^^^^^^^^
811 748
812 Function/variable namespaces improve readabili 749 Function/variable namespaces improve readability and allow easy
813 grepping. These namespaces are string prefixes 750 grepping. These namespaces are string prefixes for globally visible
814 function and variable names, including inlines 751 function and variable names, including inlines. These prefixes should
815 combine the subsystem and the component name s 752 combine the subsystem and the component name such as 'x86_comp\_',
816 'sched\_', 'irq\_', and 'mutex\_'. 753 'sched\_', 'irq\_', and 'mutex\_'.
817 754
818 This also includes static file scope functions 755 This also includes static file scope functions that are immediately put
819 into globally visible driver templates - it's 756 into globally visible driver templates - it's useful for those symbols
820 to carry a good prefix as well, for backtrace 757 to carry a good prefix as well, for backtrace readability.
821 758
822 Namespace prefixes may be omitted for local st 759 Namespace prefixes may be omitted for local static functions and
823 variables. Truly local functions, only called 760 variables. Truly local functions, only called by other local functions,
824 can have shorter descriptive names - our prima 761 can have shorter descriptive names - our primary concern is greppability
825 and backtrace readability. 762 and backtrace readability.
826 763
827 Please note that 'xxx_vendor\_' and 'vendor_xx 764 Please note that 'xxx_vendor\_' and 'vendor_xxx_` prefixes are not
828 helpful for static functions in vendor-specifi 765 helpful for static functions in vendor-specific files. After all, it
829 is already clear that the code is vendor-speci 766 is already clear that the code is vendor-specific. In addition, vendor
830 names should only be for truly vendor-specific 767 names should only be for truly vendor-specific functionality.
831 768
832 As always apply common sense and aim for consi 769 As always apply common sense and aim for consistency and readability.
833 770
834 771
835 Commit notifications 772 Commit notifications
836 -------------------- 773 --------------------
837 774
838 The tip tree is monitored by a bot for new com 775 The tip tree is monitored by a bot for new commits. The bot sends an email
839 for each new commit to a dedicated mailing lis 776 for each new commit to a dedicated mailing list
840 (``linux-tip-commits@vger.kernel.org``) and Cc 777 (``linux-tip-commits@vger.kernel.org``) and Cc's all people who are
841 mentioned in one of the commit tags. It uses t 778 mentioned in one of the commit tags. It uses the email message ID from the
842 Link tag at the end of the tag list to set the 779 Link tag at the end of the tag list to set the In-Reply-To email header so
843 the message is properly threaded with the patc 780 the message is properly threaded with the patch submission email.
844 781
845 The tip maintainers and submaintainers try to 782 The tip maintainers and submaintainers try to reply to the submitter
846 when merging a patch, but they sometimes forge 783 when merging a patch, but they sometimes forget or it does not fit the
847 workflow of the moment. While the bot message 784 workflow of the moment. While the bot message is purely mechanical, it
848 also implies a 'Thank you! Applied.'. 785 also implies a 'Thank you! Applied.'.
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