linux-kernel - Re: [PATCH] mm/swapfile.c: use spin_lock_bh with swap

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Message-ID: <20150203131437.GA8914@dhcp22.suse.cz>
Date:	Tue, 3 Feb 2015 14:14:37 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	pasi.sjoholm@...la.com
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Pasi Sjöholm <pasi.sjoholm@...lamobile.com>
Subject: Re: [PATCH] mm/swapfile.c: use spin_lock_bh with swap_lock to avoid
 deadlocks

On Mon 02-02-15 18:25:28, pasi.sjoholm@...la.com wrote:
> From: Pasi Sjöholm <pasi.sjoholm@...lamobile.com>
> 
> It is possible to get kernel in deadlock-state if swap_lock is not locked
> with spin_lock_bh by calling si_swapinfo() simultaneously through
> timer_function and registered vm shinker callback-function.
> 
> BUG: spinlock recursion on CPU#0, main/2447
> lock: swap_lock+0x0/0x10, .magic: dead4ead, .owner: main/2447, .owner_cpu: 0
> [<c010b938>] (unwind_backtrace+0x0/0x11c) from [<c03e9be0>] (do_raw_spin_lock+0x48/0x154)
> [<c03e9be0>] (do_raw_spin_lock+0x48/0x154) from [<c0226e10>] (si_swapinfo+0x10/0x90)
> [<c0226e10>] (si_swapinfo+0x10/0x90) from [<c04d7e18>] (timer_function+0x24/0x258)

Who is calling si_swapinfo from timer_function? AFAICS the vanilla
kernel doesn't do that. Or am I missing something?
-- 
Michal Hocko
SUSE Labs
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