linux-kernel - Re: [PATCH] Detect early free of a live mm

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Date:   Thu, 1 Mar 2018 17:16:09 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Michal Hocko <mhocko@...e.com>,
        Peter Zijlstra <peterz@...raded.org>,
        Rik van Riel <riel@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] Detect early free of a live mm

On Wed, 28 Feb 2018 12:14:58 +0000 Mark Rutland <mark.rutland@....com> wrote:

> KASAN splats indicate that in some cases we free a live mm, then
> continue to access it, with potentially disastrous results. This is
> likely due to a mismatched mmdrop() somewhere in the kernel, but so far
> the culprit remains elusive.
> 
> Let's have __mmdrop() verify that the mm isn't live for the current
> task, similar to the existing check for init_mm. This way, we can catch
> this class of issue earlier, and without requiring KASAN.

Presumably the results usually aren't disastrous.  But they will be if
we go and add BUG_ON()s!  Can we make this WARN_ON[_ONCE]()?  We should
still get the same info from testers.