From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org
Cc: linux-tip-commits@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
x86@kernel.org
Subject: Re: [tip: locking/urgent] locking/ww_mutex: Treat ww_mutex_lock() like a trylock
Date: Wed, 17 Mar 2021 10:03:07 -0400 [thread overview]
Message-ID: <e1bcd7fb-3a40-f207-ee19-d276c8b8bb75@redhat.com> (raw)
In-Reply-To: <YFIEo8IVQ/Mm9jUE@hirez.programming.kicks-ass.net>
On 3/17/21 9:31 AM, Peter Zijlstra wrote:
> On Wed, Mar 17, 2021 at 02:12:41PM +0100, Peter Zijlstra wrote:
>> On Wed, Mar 17, 2021 at 12:38:21PM -0000, tip-bot2 for Waiman Long wrote:
>>> + /*
>>> + * Treat as trylock for ww_mutex.
>>> + */
>>> + mutex_acquire_nest(&lock->dep_map, subclass, !!ww_ctx, nest_lock, ip);
>> I'm confused... why isn't nest_lock working here?
>>
>> For ww_mutex, we're supposed to have ctx->dep_map as a nest_lock, and
>> all lock acquisitions under a nest lock should be fine. Afaict the above
>> is just plain wrong.
> To clarify:
>
> mutex_lock(&A); ww_mutex_lock(&B, ctx);
> ww_mutex_lock(&B, ctx); mutex_lock(&A);
>
> should still very much be a deadlock, but your 'fix' makes it not report
> that.
>
> Only order within the ww_ctx can be ignored, and that's exactly what
> nest_lock should be doing.
>
I will take a deeper look into why that is the case.
Cheers,
Longman
next prev parent reply other threads:[~2021-03-17 14:04 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 15:31 [PATCH 0/4] locking/ww_mutex: Fix locktorture ww_mutex test problems Waiman Long
2021-03-16 15:31 ` [PATCH 1/4] locking/ww_mutex: Simplify use_ww_ctx & ww_ctx handling Waiman Long
2021-03-16 18:55 ` Davidlohr Bueso
2021-03-17 12:38 ` [tip: locking/urgent] " tip-bot2 for Waiman Long
2021-03-17 12:59 ` Peter Zijlstra
2021-03-17 13:43 ` Waiman Long
2021-03-17 13:55 ` Peter Zijlstra
2021-03-17 14:10 ` Waiman Long
2021-03-17 14:17 ` Peter Zijlstra
2021-03-17 14:33 ` Waiman Long
2021-03-16 15:31 ` [PATCH 2/4] locking/ww_mutex: Fix acquire/release imbalance in ww_acquire_init()/ww_acquire_fini() Waiman Long
2021-03-17 12:38 ` [tip: locking/urgent] " tip-bot2 for Waiman Long
2021-03-16 15:31 ` [PATCH 3/4] locking/ww_mutex: Treat ww_mutex_lock() like a trylock Waiman Long
2021-03-17 3:01 ` Davidlohr Bueso
2021-03-17 12:38 ` [tip: locking/urgent] " tip-bot2 for Waiman Long
2021-03-17 13:12 ` Peter Zijlstra
2021-03-17 13:31 ` Peter Zijlstra
2021-03-17 14:03 ` Waiman Long [this message]
2021-03-17 15:35 ` Waiman Long
2021-03-17 16:48 ` Peter Zijlstra
2021-03-17 17:40 ` Peter Zijlstra
2021-03-17 17:45 ` Peter Zijlstra
2021-03-17 18:32 ` Waiman Long
2021-03-17 19:58 ` Peter Zijlstra
2021-03-17 20:20 ` Waiman Long
2021-03-17 18:14 ` Waiman Long
2021-03-18 2:24 ` [PATCH 3/4] " Boqun Feng
2021-03-18 2:54 ` Waiman Long
2021-03-18 6:36 ` Boqun Feng
2021-03-16 15:31 ` [PATCH 4/4] locking/locktorture: Fix incorrect use of ww_acquire_ctx in ww_mutex test Waiman Long
2021-03-17 5:16 ` Davidlohr Bueso
2021-03-17 13:21 ` Waiman Long
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