linux-kernel - Re: recursive locking (coredump/vfs

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Date:	Fri, 22 Nov 2013 22:11:56 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dave Jones <davej@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: recursive locking (coredump/vfs_write)

  Hi,

On Wed 13-11-13 16:11:47, Dave Jones wrote:
> here's another one..
> 
> 
> =============================================
> [ INFO: possible recursive locking detected ]
> 3.12.0+ #2 Not tainted
> ---------------------------------------------
> trinity-child3/13302 is trying to acquire lock:
>  (sb_writers#5){.+.+.+}, at: [<ffffffff811b7013>] vfs_write+0x173/0x1f0
> 
> but task is already holding lock:
>  (sb_writers#5){.+.+.+}, at: [<ffffffff8122006d>] do_coredump+0xf1d/0x1070
  Thanks for report. Attached patch should fix this. Al, can you please
merge it?

								Honza

> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(sb_writers#5);
>   lock(sb_writers#5);
> 
>  *** DEADLOCK ***
> 
>  May be due to missing lock nesting notation
> 
> 1 lock held by trinity-child3/13302:
>  #0:  (sb_writers#5){.+.+.+}, at: [<ffffffff8122006d>] do_coredump+0xf1d/0x1070
> 
> stack backtrace:
> CPU: 3 PID: 13302 Comm: trinity-child3 Not tainted 3.12.0+ #2 
>  ffffffff82526e10 ffff8801b54af820 ffffffff8171b3dc ffffffff82526e10
>  ffff8801b54af8e0 ffffffff810d722b 00007f93d6ce5000 0000000000000000
>  ffff880154b3f200 ffff880100000000 00000000004da26d ffffffff821b3901
> Call Trace:
>  [<ffffffff8171b3dc>] dump_stack+0x4e/0x7a
>  [<ffffffff810d722b>] __lock_acquire+0x19ab/0x19f0
>  [<ffffffff81729334>] ? __do_page_fault+0x264/0x610
>  [<ffffffff8100b144>] ? native_sched_clock+0x24/0x80
>  [<ffffffff810d1d1f>] ? trace_hardirqs_off_caller+0x1f/0xc0
>  [<ffffffff810d7a23>] lock_acquire+0x93/0x1c0
>  [<ffffffff811b7013>] ? vfs_write+0x173/0x1f0
>  [<ffffffff811b97f9>] __sb_start_write+0xc9/0x1a0
>  [<ffffffff811b7013>] ? vfs_write+0x173/0x1f0
>  [<ffffffff811b7013>] ? vfs_write+0x173/0x1f0
>  [<ffffffff812cc303>] ? security_file_permission+0x23/0xa0
>  [<ffffffff811b7013>] vfs_write+0x173/0x1f0
>  [<ffffffff8121ef02>] dump_emit+0x92/0xd0
>  [<ffffffff81218d50>] elf_core_dump+0xde0/0x1740
>  [<ffffffff81218832>] ? elf_core_dump+0x8c2/0x1740
>  [<ffffffff8121fdee>] do_coredump+0xc9e/0x1070
>  [<ffffffff81719d9b>] ? __slab_free+0x191/0x35d
>  [<ffffffff8106a9b8>] get_signal_to_deliver+0x2c8/0x930
>  [<ffffffff810024b8>] do_signal+0x48/0x610
>  [<ffffffff810d1e39>] ? get_lock_stats+0x19/0x60
>  [<ffffffff810d25ae>] ? put_lock_stats.isra.28+0xe/0x30
>  [<ffffffff81715e86>] ? pagefault_enable+0xe/0x21
>  [<ffffffff8114b86e>] ? context_tracking_user_exit+0x4e/0x190
>  [<ffffffff810d54c5>] ? trace_hardirqs_on_caller+0x115/0x1e0
>  [<ffffffff81002adc>] do_notify_resume+0x5c/0xa0
>  [<ffffffff81725f86>] retint_signal+0x46/0x90
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR

View attachment "0001-coredump-Avoid-fs-freezing-deadlock-when-dumping-cor.patch" of type "text/x-patch" (1292 bytes)