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Re: !PageLocked from shmem charge path hits VM_BUG_ON with 4.4-rc4

From Michal Hocko <mhocko@kernel.org>
Newsgroups linux.kernel
Subject Re: !PageLocked from shmem charge path hits VM_BUG_ON with 4.4-rc4
Date 2015-12-14 13:10 +0100
Message-ID <qFA6Z-5XO-9@gated-at.bofh.it> (permalink)
References <qFyeU-4Fp-41@gated-at.bofh.it> <qFzaW-5m6-17@gated-at.bofh.it>
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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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Re: !PageLocked from shmem charge path hits VM_BUG_ON with 4.4-rc4 Michal Hocko <mhocko@kernel.org> - 2015-12-14 12:10 +0100
  Re: !PageLocked from shmem charge path hits VM_BUG_ON with 4.4-rc4 Michal Hocko <mhocko@kernel.org> - 2015-12-14 13:10 +0100

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