* [PATCH v2] nptl: pthread_rwlock_rdlock return in low priority
@ 2023-03-07 11:38 abush wang
2023-03-07 11:49 ` Xi Ruoyao
0 siblings, 1 reply; 3+ messages in thread
From: abush wang @ 2023-03-07 11:38 UTC (permalink / raw)
To: drepper.fsp, abushwang via Libc-alpha
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(*This is just a mail for advisory*)
hi, I have noticed reader will return directly on fast-path in
pthread_rwlock_common.c
>* /* We have registered as a reader, so if we are in a read phase, we have
*>* acquired a read lock. This is also the reader--reader fast-path.
*>* Even if there is a primary writer, we just return. If writers are to
*>* be preferred and we are the only active reader, we could try to enter a
*>* write phase to let the writer proceed. This would be okay because we
*>* cannot have acquired the lock previously as a reader (which could result
*>* in deadlock if we would wait for the primary writer to run). However,
*>* this seems to be a corner case and handling it specially not
be worth the
*>* complexity. */
*>* if (__glibc_likely ((r & PTHREAD_RWLOCK_WRPHASE) == 0))
*>* return 0;
*
However, there is a situation:
main, thread_wr, thread_rd.
SCHED_FIFO priority:
main > thread_wr > thread_rd
main first acquires read lock, then create thread_wr which will
block on the lock.
Next, main creates thread_rd. this thread will acquires read lock
on fast-path even
though it has a lower priority compared to thread_wr.
You can get demo from the following
repository:https://github.com/emscripten-core/posixtestsuite.git
./conformance/interfaces/pthread_rwlock_rdlock/2-1.c
According to "man -M man-pages-posix-2017/ 3p pthread_rwlock_rdlock"
>* DESCRIPTION
*>* The pthread_rwlock_rdlock() function shall apply a read lock to the
*>* read-write lock referenced by rwlock. The calling thread acquires the
*>* read lock if a writer does not hold the lock and there are no
*>* writers blocked on the lock.
*>>* If the Thread Execution Scheduling option is supported, and the
*>* threads involved in the lock are executing with the scheduling
*>* policies SCHED_FIFO or SCHED_RR, the calling thread shall not acquire
*>* the lock if a writer holds the lock or if writers of higher or equal
*>* priority are blocked on the lock; other‐ wise, the calling thread
*>* shall acquire the lock.
*
I was wondering that whether this fast-path is reasonable, and whether
this posix standard should be enforced.
Thanks
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] nptl: pthread_rwlock_rdlock return in low priority
2023-03-07 11:38 [PATCH v2] nptl: pthread_rwlock_rdlock return in low priority abush wang
@ 2023-03-07 11:49 ` Xi Ruoyao
2023-03-07 12:08 ` abush wang
0 siblings, 1 reply; 3+ messages in thread
From: Xi Ruoyao @ 2023-03-07 11:49 UTC (permalink / raw)
To: abush wang, drepper.fsp, abushwang via Libc-alpha
On Tue, 2023-03-07 at 19:38 +0800, abush wang via Libc-alpha wrote:
> (*This is just a mail for advisory*)
Do not overuse git send-email anymore. By adding [PATCH] in the title
your message appears as a junk in the patchwork interface.
If you can't use another CLI tool, stop preventing you are clever and go
to use a normal mail client. This is just annoying.
--
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] nptl: pthread_rwlock_rdlock return in low priority
2023-03-07 11:49 ` Xi Ruoyao
@ 2023-03-07 12:08 ` abush wang
0 siblings, 0 replies; 3+ messages in thread
From: abush wang @ 2023-03-07 12:08 UTC (permalink / raw)
To: Xi Ruoyao; +Cc: drepper.fsp, abushwang via Libc-alpha
[-- Attachment #1: Type: text/plain, Size: 640 bytes --]
this message is from gmail.
Please pay attention on this issue,
Xi Ruoyao <xry111@xry111.site> 于2023年3月7日周二 19:49写道:
> On Tue, 2023-03-07 at 19:38 +0800, abush wang via Libc-alpha wrote:
> > (*This is just a mail for advisory*)
>
> Do not overuse git send-email anymore. By adding [PATCH] in the title
> your message appears as a junk in the patchwork interface.
>
> If you can't use another CLI tool, stop preventing you are clever and go
> to use a normal mail client. This is just annoying.
>
> --
> Xi Ruoyao <xry111@xry111.site>
> School of Aerospace Science and Technology, Xidian University
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-03-07 11:38 [PATCH v2] nptl: pthread_rwlock_rdlock return in low priority abush wang
2023-03-07 11:49 ` Xi Ruoyao
2023-03-07 12:08 ` abush wang
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