linux-kernel - Re: !PageLocked from shmem charge path hits VM_BUG

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Date:	Mon, 14 Dec 2015 13:06:22 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Daniel Vetter <daniel.vetter@...el.com>,
	David Airlie <airlied@...ux.ie>,
	Mika Westerber <mika.westerberg@...el.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: !PageLocked from shmem charge path hits VM_BUG_ON with 4.4-rc4

On Mon 14-12-15 12:03:20, Michal Hocko wrote:
> JFYI: Andrey Ryabinin has noticed that this might be related to
> http://lkml.kernel.org/r/CAPAsAGzrOQAABhOta_o-MzocnikjPtwJLfEKQJ3n5mbBm0T7Bw@mail.gmail.com
> 
> and indeed if somebody with pending signals would do wait_on_page_locked
> then it could race AFAIU.

No, a simple lock_page would fail to lock the page (thanks Andrey for
the clarification in the parallel email thread). I have missed that
__lock_page uses bit_wait_io and that would return EINTR when using
signal_pending. The fix has changed that to singnal_pending_state so
this will not happen anymore. I think the mystery is solved...

-- 
Michal Hocko
SUSE Labs
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