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From: Peter Zijlstra <peterz@infradead.org>
To: "Christian König" <christian.koenig@amd.com>
Cc: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu
Date: Tue, 20 Feb 2018 14:22:54 +0100	[thread overview]
Message-ID: <20180220132254.GB25201@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <c22fe062-6c7e-cfa3-5f0b-da135a751921@amd.com>

On Tue, Feb 20, 2018 at 02:08:26PM +0100, Christian König wrote:
> Am 20.02.2018 um 13:35 schrieb Peter Zijlstra:
> > > +static inline bool ww_mutex_is_owned_by(struct ww_mutex *lock,
> > > +					struct task_struct *task,
> > > +					struct ww_acquire_ctx *ctx)
> > > +{
> > > +	return likely(__mutex_owner(&lock->base) == task) &&
> > > +		READ_ONCE(lock->ctx) == ctx;
> > > +}
> > Nak on that interface, that's racy and broken by design.
> 
> Why?

If task != current you can race with a concurrent mutex_unlock().
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: "Christian König" <christian.koenig@amd.com>
Cc: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu
Date: Tue, 20 Feb 2018 14:22:54 +0100	[thread overview]
Message-ID: <20180220132254.GB25201@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <c22fe062-6c7e-cfa3-5f0b-da135a751921@amd.com>

On Tue, Feb 20, 2018 at 02:08:26PM +0100, Christian König wrote:
> Am 20.02.2018 um 13:35 schrieb Peter Zijlstra:
> > > +static inline bool ww_mutex_is_owned_by(struct ww_mutex *lock,
> > > +					struct task_struct *task,
> > > +					struct ww_acquire_ctx *ctx)
> > > +{
> > > +	return likely(__mutex_owner(&lock->base) == task) &&
> > > +		READ_ONCE(lock->ctx) == ctx;
> > > +}
> > Nak on that interface, that's racy and broken by design.
> 
> Why?

If task != current you can race with a concurrent mutex_unlock().

  reply	other threads:[~2018-02-20 13:22 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-15 14:19 [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu Christian König
2018-02-15 14:19 ` Christian König
2018-02-15 14:19 ` [PATCH 2/3] drm/ttm: handle already locked BOs during eviction and swapout Christian König
     [not found] ` <20180215141944.4332-1-christian.koenig-5C7GfCeVMHo@public.gmane.org>
2018-02-15 14:19   ` [PATCH 3/3] drm/ttm: keep BOs reserved until end of eviction Christian König
2018-02-15 14:19     ` Christian König
2018-02-15 20:36 ` [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu Alex Deucher
2018-02-15 20:36   ` Alex Deucher
2018-02-19 15:24 ` Daniel Vetter
2018-02-19 15:24   ` Daniel Vetter
     [not found]   ` <20180219152421.GQ22199-dv86pmgwkMBes7Z6vYuT8azUEOm+Xw19@public.gmane.org>
2018-02-19 15:41     ` Christian König
2018-02-19 15:41       ` Christian König
     [not found]       ` <cbfec1ed-d01f-1d4f-c3c0-cc04b93bc58c-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-02-19 16:15         ` Daniel Vetter
2018-02-19 16:15           ` Daniel Vetter
2018-02-19 16:29           ` Christian König
2018-02-19 16:29             ` Christian König
2018-02-19 16:43             ` Daniel Vetter
2018-02-19 16:43               ` Daniel Vetter
     [not found]               ` <20180219164354.GB22199-dv86pmgwkMBes7Z6vYuT8azUEOm+Xw19@public.gmane.org>
2018-02-20  9:43                 ` Christian König
2018-02-20  9:43                   ` Christian König
     [not found]                   ` <f3cef14f-135c-2446-74b5-20e14773b0c4-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-02-20 11:33                     ` Daniel Vetter
2018-02-20 11:33                       ` Daniel Vetter
     [not found]                       ` <20180220113318.GN22199-dv86pmgwkMBes7Z6vYuT8azUEOm+Xw19@public.gmane.org>
2018-02-20 12:31                         ` Christian König
2018-02-20 12:31                           ` Christian König
2018-02-20 12:35 ` Peter Zijlstra
2018-02-20 12:35   ` Peter Zijlstra
2018-02-20 13:08   ` Christian König
2018-02-20 13:08     ` Christian König
2018-02-20 13:22     ` Peter Zijlstra [this message]
2018-02-20 13:22       ` Peter Zijlstra

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