kernel/linux.git/include/linux/seqlock.h, branch v5.11.6

seqlock: kernel-doc: Specify when preemption is automatically altered

2020-12-09T16:08:49+00:00

The kernel-doc annotations for sequence counters write side functions are incomplete: they do not specify when preemption is automatically disabled and re-enabled. This has confused a number of call-site developers. Fix it. Signed-off-by: Ahmed S. Darwish Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/CAHk-=wikhGExmprXgaW+MVXG1zsGpztBbVwOb23vetk41EtTBQ@mail.gmail.com

seqlock: Prefix internal seqcount_t-only macros with a "do_"

2020-12-09T16:08:49+00:00

When the seqcount_LOCKNAME_t group of data types were introduced, two classes of seqlock.h sequence counter macros were added: - An external public API which can either take a plain seqcount_t or any of the seqcount_LOCKNAME_t variants. - An internal API which takes only a plain seqcount_t. To distinguish between the two groups, the "*_seqcount_t_*" pattern was used for the latter. This confused a number of mm/ call-site developers, and Linus also commented that it was not a standard practice for marking seqlock.h internal APIs. Distinguish the latter group of macros by prefixing a "do_". Signed-off-by: Ahmed S. Darwish Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/CAHk-=wikhGExmprXgaW+MVXG1zsGpztBbVwOb23vetk41EtTBQ@mail.gmail.com

seqlock: Rename __seqprop() users

2020-12-03T10:20:51+00:00

More consistent naming should make it easier to untangle the _Generic token pasting maze called __seqprop(). Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20201110115358.GE2594@hirez.programming.kicks-ass.net

seqlock: avoid -Wshadow warnings

2020-12-03T10:20:50+00:00

When building with W=2, there is a flood of warnings about the seqlock macros shadowing local variables: 19806 linux/seqlock.h:331:11: warning: declaration of 'seq' shadows a previous local [-Wshadow] 48 linux/seqlock.h:348:11: warning: declaration of 'seq' shadows a previous local [-Wshadow] 8 linux/seqlock.h:379:11: warning: declaration of 'seq' shadows a previous local [-Wshadow] Prefix the local variables to make the warning useful elsewhere again. Fixes: 52ac39e5db51 ("seqlock: seqcount_t: Implement all read APIs as statement expressions") Signed-off-by: Arnd Bergmann Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20201026165044.3722931-1-arnd@kernel.org

locking/seqlocks: Fix kernel-doc warnings

2020-10-14T16:07:50+00:00

Right now, seqlock.h produces kernel-doc warnings: ./include/linux/seqlock.h:181: error: Cannot parse typedef! Convert it to a plain comment to avoid confusing kernel-doc. Fixes: a8772dccb2ec ("seqlock: Fold seqcount_LOCKNAME_t definition") Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/a59144cdaadf7fdf1fe5d55d0e1575abbf1c0cb3.1602590106.git.mchehab+huawei@kernel.org

locking/seqlock: Tweak DEFINE_SEQLOCK() kernel doc

2020-10-07T16:14:14+00:00

ctags creates a warning: |ctags: Warning: include/linux/seqlock.h:738: null expansion of name pattern "\2" The DEFINE_SEQLOCK() macro is passed to ctags and being told to expect an argument. Add a dummy argument to keep ctags quiet. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Acked-by: Will Deacon Link: https://lkml.kernel.org/r/20200924154851.skmswuyj322yuz4g@linutronix.de

seqlock: Unbreak lockdep

2020-09-16T14:26:58+00:00

seqcount_LOCKNAME_init() needs to be a macro due to the lockdep annotation in seqcount_init(). Since a macro cannot define another macro, we need to effectively revert commit: e4e9ab3f9f91 ("seqlock: Fold seqcount_LOCKNAME_init() definition"). Fixes: e4e9ab3f9f91 ("seqlock: Fold seqcount_LOCKNAME_init() definition") Reported-by: Qian Cai Debugged-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Tested-by: Qian Cai Link: https://lkml.kernel.org/r/20200915143028.GB2674@hirez.programming.kicks-ass.net

seqlock: PREEMPT_RT: Do not starve seqlock_t writers

2020-09-10T09:19:31+00:00

On PREEMPT_RT, seqlock_t is transformed to a sleeping lock that do not disable preemption. A seqlock_t reader can thus preempt its write side section and spin for the enter scheduler tick. If that reader belongs to a real-time scheduling class, it can spin forever and the kernel will livelock. To break this livelock possibility on PREEMPT_RT, implement seqlock_t in terms of "seqcount_spinlock_t" instead of plain "seqcount_t". Beside its pure annotational value, this will leverage the existing seqcount_LOCKNAME_T PREEMPT_RT anti-livelock mechanisms, without adding any extra code. Signed-off-by: Ahmed S. Darwish Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200904153231.11994-6-a.darwish@linutronix.de

seqlock: seqcount_LOCKNAME_t: Introduce PREEMPT_RT support

2020-09-10T09:19:31+00:00

Preemption must be disabled before entering a sequence counter write side critical section. Otherwise the read side section can preempt the write side section and spin for the entire scheduler tick. If that reader belongs to a real-time scheduling class, it can spin forever and the kernel will livelock. Disabling preemption cannot be done for PREEMPT_RT though: it can lead to higher latencies, and the write side sections will not be able to acquire locks which become sleeping locks (e.g. spinlock_t). To remain preemptible, while avoiding a possible livelock caused by the reader preempting the writer, use a different technique: let the reader detect if a seqcount_LOCKNAME_t writer is in progress. If that's the case, acquire then release the associated LOCKNAME writer serialization lock. This will allow any possibly-preempted writer to make progress until the end of its writer serialization lock critical section. Implement this lock-unlock technique for all seqcount_LOCKNAME_t with an associated (PREEMPT_RT) sleeping lock. References: 55f3560df975 ("seqlock: Extend seqcount API with associated locks") Signed-off-by: Ahmed S. Darwish Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200519214547.352050-1-a.darwish@linutronix.de

seqlock: seqcount_t: Implement all read APIs as statement expressions

2020-09-10T09:19:31+00:00

The sequence counters read APIs are implemented as CPP macros, so they can take either seqcount_t or any of the seqcount_LOCKNAME_t variants. Such macros then get *directly* transformed to internal C functions that only take plain seqcount_t. Further commits need access to seqcount_LOCKNAME_t inside of the actual read APIs code. Thus transform all of the seqcount read APIs to pure GCC statement expressions instead. This will not break type-safety: all of the transformed APIs resolve to a _Generic() selection that does not have a "default" case. This will also not affect the transformed APIs readability: previously added kernel-doc above all of seqlock.h functions makes the expectations quite clear for call-site developers. Signed-off-by: Ahmed S. Darwish Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200904153231.11994-4-a.darwish@linutronix.de