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From: peterz@infradead.org
To: Qian Cai <cai@lca.pw>
Cc: mark.rutland@arm.com, akpm@linux-foundation.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH -next] fork: silence a false postive warning in __mmdrop
Date: Tue, 8 Sep 2020 19:58:08 +0200	[thread overview]
Message-ID: <20200908175808.GX1362448@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200908165043.GD5147@lca.pw>

On Tue, Sep 08, 2020 at 12:50:44PM -0400, Qian Cai wrote:
> > No, you're talking nonsense. We must not free @mm when
> > 'current->active_mm == mm', never.
> 
> Yes, you are right. It still trigger this below on powerpc with today's
> linux-next by fuzzing for a while (saw a few times on recent linux-next before
> as well but so far mostly reproducible on powerpc here). Any idea?

If you can reliably reproduce this, the next thing is to trace mm_count
and figure out where it goes side-ways. I suppose we're looking for an
'extra' decrement.

Mark tried this for a while but gave up because he couldn't reliably
reproduce.

WARNING: multiple messages have this Message-ID
From: peterz@infradead.org
To: Qian Cai <cai@lca.pw>
Cc: mark.rutland@arm.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, akpm@linux-foundation.org,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH -next] fork: silence a false postive warning in __mmdrop
Date: Tue, 8 Sep 2020 19:58:08 +0200	[thread overview]
Message-ID: <20200908175808.GX1362448@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200908165043.GD5147@lca.pw>

On Tue, Sep 08, 2020 at 12:50:44PM -0400, Qian Cai wrote:
> > No, you're talking nonsense. We must not free @mm when
> > 'current->active_mm == mm', never.
> 
> Yes, you are right. It still trigger this below on powerpc with today's
> linux-next by fuzzing for a while (saw a few times on recent linux-next before
> as well but so far mostly reproducible on powerpc here). Any idea?

If you can reliably reproduce this, the next thing is to trace mm_count
and figure out where it goes side-ways. I suppose we're looking for an
'extra' decrement.

Mark tried this for a while but gave up because he couldn't reliably
reproduce.

  reply	other threads:[~2020-09-08 17:58 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-04 15:03 Qian Cai
2020-07-21 17:30 ` Qian Cai
2020-07-22 10:06 ` peterz
2020-07-22 13:19   ` Qian Cai
2020-07-22 13:44     ` Peter Zijlstra
2020-09-08 16:50       ` Qian Cai
2020-09-08 16:50         ` Qian Cai
2020-09-08 17:58         ` peterz [this message]
2020-09-08 17:58           ` peterz

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