linux-kernel - Re: [PATCH] locking/mutex: Disable preemption in __mutex_unlock

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Message-ID: <700c49da-1e30-4b99-ad41-3b052c80b64b@redhat.com>
Date: Wed, 9 Jul 2025 15:42:46 -0400
From: Waiman Long <llong@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
 Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH] locking/mutex: Disable preemption in
 __mutex_unlock_slowpath()


On 7/9/25 2:28 PM, Linus Torvalds wrote:
> On Wed, 9 Jul 2025 at 11:21, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>> And I suspect it would involve the exact *opposite* of your patch:
>> make mutex_unlock() actively cause preemption after it has released
>> the lock but before it has done the final accesses.
> .. sadly, I suspect we have a ton of mutex_unlock() users in atomic
> contexts, so we probably can't do that. It's not like you *should* do
> it, but I don't think we've ever disallowed it.
>
> You can't use mutex_unlock from interrupts etc, but you can use it
> while holding a spinlock.

I have just sent out another mutex patch to enforce a context switch in 
__mutex_unlock_slowpath() under the right context.

As for this one, you are right that hiding it may not be the best idea. 
So I am going to drop it.

Cheers,
Longman