linux-kernel - Re: Warning from kernel/printk/printk.c in linux-next

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Date:	Tue, 29 Apr 2014 23:11:28 +0200
From:	Jan Kara <jack@...e.cz>
To:	Fabio Estevam <festevam@...il.com>
Cc:	jack@...e.cz, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Warning from kernel/printk/printk.c in linux-next

  Hello,

On Tue 29-04-14 13:33:17, Fabio Estevam wrote:
> I am running linux-next 20140429 on a mx6 board (ARM 32-bit) and after commit
> 5dc90cb49691755faa ("printk: enable interrupts before calling
> console_trylock_for_printk()") I get the following warning:
  Thanks for report. Attached patch should fix the problem I hope.

								Honza

> [ INFO: possible recursive locking detected ]
> 3.15.0-rc3-next-20140429-00001-gac246a5 #1074 Not tainted
> ---------------------------------------------
> swapper/0/0 is trying to acquire lock:
>  (console_lock){+.+...}, at: [<808c1358>] con_init+0x14/0x29c
> 
> but task is already holding lock:
>  (console_lock){+.+...}, at: [<8006deac>] vprintk_emit+0x194/0x514
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(console_lock);
>   lock(console_lock);
> 
>  *** DEADLOCK ***
> 
>  May be due to missing lock nesting notation
> 
> 1 lock held by swapper/0/0:
>  #0:  (console_lock){+.+...}, at: [<8006deac>] vprintk_emit+0x194/0x514
> 
> stack backtrace:
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.15.0-rc3-next-20140429-00001-gac2464
> Backtrace:
> [<80011cbc>] (dump_backtrace) from [<80011e58>] (show_stack+0x18/0x1c)
>  r6:8114b4fc r5:00000000 r4:00000000 r3:00000000
> [<80011e40>] (show_stack) from [<8065e65c>] (dump_stack+0x88/0xa4)
> [<8065e5d4>] (dump_stack) from [<80065518>] (__lock_acquire+0x1494/0x1c10)
>  r5:808f3f70 r4:80a7d6c0
> [<80064084>] (__lock_acquire) from [<80066178>] (lock_acquire+0x68/0x7c)
>  r10:00000000 r9:412fc09a r8:8000406a r7:00000001 r6:60000153 r5:808e8000
>  r4:00000000
> [<80066110>] (lock_acquire) from [<8006c91c>] (console_lock+0x54/0x68)
>  r7:befffbc0 r6:808d6db0 r5:808c1358 r4:00000001
> [<8006c8c8>] (console_lock) from [<808c1358>] (con_init+0x14/0x29c)
>  r5:808e37a4 r4:808e37a4
> [<808c1344>] (con_init) from [<808c0ae4>] (console_init+0x24/0x38)
>  r6:808d6db0 r5:808e37a4 r4:808e37a4
> [<808c0ac0>] (console_init) from [<80894bb4>] (start_kernel+0x26c/0x3a4)
>  r5:8094d5c0 r4:ffffffff
> [<80894948>] (start_kernel) from [<80008074>] (0x80008074)
>  r7:808f5644 r6:808d6dac r5:808f0928 r4:10c5387d
> 
> Reverting this commit causes the warning to go away.
> 
> Any suggestions?
> 
> Regards,
> 
> Fabio Estevam
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR

View attachment "0001-printk-Fix-lockdep-instrumentation-of-console_sem.patch" of type "text/x-patch" (3959 bytes)