Messages in this thread | | | Date | Mon, 5 Jul 2021 16:00:01 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 1/4] locking/mutex: Use try_cmpxchg() |
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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.
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