linux-kernel - Re: [PATCH] fbcon: fix lockdep warning from fbcon

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Date:	Mon, 13 Sep 2010 15:21:27 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fbcon: fix lockdep warning from fbcon_deinit()

On Mon, 13 Sep 2010 23:58:50 +0200
Jarek Poplawski <jarkao2@...il.com> wrote:

> This patch fixes the lockdep warning:
> 
> [   13.657164] INFO: trying to register non-static key.
> [   13.657169] the code is fine but needs lockdep annotation.
> [   13.657171] turning off the locking correctness validator.
> [   13.657177] Pid: 622, comm: modprobe Not tainted 2.6.36-rc3c #8
> [   13.657180] Call Trace:
> [   13.657194]  [<c13002c8>] ? printk+0x18/0x20
> [   13.657202]  [<c1056cf6>] register_lock_class+0x336/0x350
> [   13.657208]  [<c1058bf9>] __lock_acquire+0x449/0x1180
> [   13.657215]  [<c1059997>] lock_acquire+0x67/0x80
> [   13.657222]  [<c1042bf1>] ? __cancel_work_timer+0x51/0x230
> [   13.657227]  [<c1042c23>] __cancel_work_timer+0x83/0x230
> [   13.657231]  [<c1042bf1>] ? __cancel_work_timer+0x51/0x230
> [   13.657236]  [<c10582b2>] ? mark_held_locks+0x62/0x80
> [   13.657243]  [<c10b3a2f>] ? kfree+0x7f/0xe0
> [   13.657248]  [<c105853c>] ? trace_hardirqs_on_caller+0x11c/0x160
> [   13.657253]  [<c105858b>] ? trace_hardirqs_on+0xb/0x10
> [   13.657259]  [<c117f4cd>] ? fbcon_deinit+0x16d/0x1e0
> [   13.657263]  [<c117f4cd>] ? fbcon_deinit+0x16d/0x1e0
> [   13.657268]  [<c1042dea>] cancel_work_sync+0xa/0x10
> [   13.657272]  [<c117f444>] fbcon_deinit+0xe4/0x1e0
> ...
> 
> The warning is caused by trying to cancel an uninitialized work from
> fbcon_exit(). Fix it by adding a check for queue.func, similarly to
> other places in this code.
> 
> Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
> ---
> 
> diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
> index 84f8423..7ccc967 100644
> --- a/drivers/video/console/fbcon.c
> +++ b/drivers/video/console/fbcon.c
> @@ -3508,7 +3508,7 @@ static void fbcon_exit(void)
>  	softback_buf = 0UL;
>  
>  	for (i = 0; i < FB_MAX; i++) {
> -		int pending;
> +		int pending = 0;
>  
>  		mapped = 0;
>  		info = registered_fb[i];
> @@ -3516,7 +3516,8 @@ static void fbcon_exit(void)
>  		if (info == NULL)
>  			continue;
>  
> -		pending = cancel_work_sync(&info->queue);
> +		if (info->queue.func)
> +			pending = cancel_work_sync(&info->queue);
>  		DPRINTK("fbcon: %s pending work\n", (pending ? "canceled" :
>  			"no"));
>  

Well.  It'd be better to just initialise the dang thing.

But all that code looks really hacky, fiddling around inside workqueue
internals as a driver-private state variable.  Needs a rewrite, I suspect.

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