From: "Xu, Yanfei" <yanfei.xu@windriver.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@redhat.com, longman@redhat.com, boqun.feng@gmail.com,
will@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 1/4] locking/mutex: Use try_cmpxchg()
Date: Mon, 5 Jul 2021 22:52:34 +0800 [thread overview]
Message-ID: <320cf54f-719c-8aa5-17af-455a53db4478@windriver.com> (raw)
In-Reply-To: <YOMQYQr1loxIuZbU@hirez.programming.kicks-ass.net>
On 7/5/21 10:00 PM, Peter Zijlstra wrote:
> [Please note: This e-mail is from an EXTERNAL e-mail address]
>
> On Mon, Jul 05, 2021 at 07:59:12PM +0800, Xu, Yanfei wrote:
>>
>>
>> On 6/30/21 11:35 PM, Peter Zijlstra wrote:
>>> For simpler and better code.
>>>
>>> Signed-off-by: Peter Zijlstra (Intel)<peterz@infradead.org>
>>> ---
>>> kernel/locking/mutex.c | 27 ++++++---------------------
>>> 1 file changed, 6 insertions(+), 21 deletions(-)
>>
>> Hi Peter,
>>
>> I read the mutex codes today, and find there seems something wrong for the
>> patch. Should we consider the race condition as blow?
>>
>> From 4035f50c96e17cbe3febab768b64da5c000e5b76 Mon Sep 17 00:00:00 2001
>> From: Yanfei Xu <yanfei.xu@windriver.com>
>> Date: Mon, 5 Jul 2021 17:56:58 +0800
>> Subject: [PATCH] locking/mutex: fix the endless loop when racing against
>> mutex.owner
>>
>> if a race condition happened on mutex.owner after we fetch its value,
>> atomic_long_try_cmpxchg_acquire/release invoked on &mutex.owner will
>> return false. Then we need to reassign the temporary variable which
>> saves mutex.owner value if in loop, or it will lead an endless loop.
>
> No, when try_cmpxchg() fails it will update oldp. This is the reason old
> is now a pointer too.
Got it. Thanks!
Yanfei
>
next prev parent reply other threads:[~2021-07-05 14:52 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-30 15:35 [RFC][PATCH 0/4] locking/mutex: Some HANDOFF fixes Peter Zijlstra
2021-06-30 15:35 ` [RFC][PATCH 1/4] locking/mutex: Use try_cmpxchg() Peter Zijlstra
2021-07-05 11:59 ` Xu, Yanfei
2021-07-05 14:00 ` Peter Zijlstra
2021-07-05 14:52 ` Xu, Yanfei [this message]
2021-07-05 15:07 ` [PATCH] Documentation/atomic_t: Document cmpxchg() vs try_cmpxchg() Peter Zijlstra
2021-07-05 15:21 ` Will Deacon
2021-07-05 15:25 ` Xu, Yanfei
2021-07-05 17:12 ` Peter Zijlstra
2021-07-08 8:42 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-07-08 8:42 ` [tip: locking/core] locking/mutex: Use try_cmpxchg() tip-bot2 for Peter Zijlstra
2021-06-30 15:35 ` [RFC][PATCH 2/4] locking/mutex: Fix HANDOFF condition Peter Zijlstra
2021-07-08 8:42 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-06-30 15:35 ` [RFC][PATCH 3/4] locking/mutex: Introduce __mutex_trylock_or_handoff() Peter Zijlstra
2021-06-30 16:30 ` Waiman Long
2021-06-30 18:04 ` Peter Zijlstra
2021-07-08 8:42 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-06-30 15:35 ` [RFC][PATCH 4/4] locking/mutex: Add MUTEX_WARN_ON Peter Zijlstra
2021-07-08 8:42 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-06-30 19:03 ` [RFC][PATCH 0/4] locking/mutex: Some HANDOFF fixes Waiman Long
2021-07-01 2:11 ` Xu, Yanfei
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