linux-kernel - Re: [PATCH] scsi_lib.c: sleeping function called from invalid context

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Date:	Thu, 24 Sep 2009 15:56:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	iceberg <strakh@...ras.ru>
Cc:	James.Bottomley@...senpartnership.com, eric@...ante.org,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi_lib.c: sleeping function called from invalid
 context

On Wed, 23 Sep 2009 17:58:47 +0000
iceberg <strakh@...ras.ru> wrote:

> Driver scsi_lib.c might sleep in atomic context, because it calls 
> scsi_device_put under spin_lock_irqsave.
> drivers/scsi/scsi_lib.c:356:
> 	spin_lock_irqsave(shost->host_lock, flags);
> 	scsi_device_put(sdev);
> Path to might_sleep macro from scsi_device_put:
> 1. scsi_device_put calls put_device at ./drivers/scsi/scsi.c:1111 
> 2. put_device calls kobject_put at ./drivers/base/core.c:1038 
> 3. kobject_put calls kref_put at ./lib/kobject.c
> 4. kref_put may call callback function kobject_release at ./lib/kref.c if 
> refcount becomes zero, which might_sleep because it calls user event. Details:
> 	4.1 kobject_cleanup calls kobject_uevent at ./lib/kobject.c:555
> 	4.2 kobject_uevent calls kobject_uevent_env at  ./lib/kobject_uevent.c:282
> 	4.3 kobject_uevent_env calls call_usermodehelper_exec at 
> ./include/linux/kmod.h:83
> 	4.4 call_usermodehelper_exec calls wait_for_completion at 
> ./kernel/kmod.c:481
> 	4.5 wait_for_completion calls wait_for_common at ./kernel/sched.c:5710
> 	4.5 wait_for_common calls might_sleep at ./kernels/sched.c:5692
> 
> Found by Linux Driver Verification project.
> 
> Delete wrong sleeping function calls.
> 
> Signed-off-by: Alexander Strakh <strakh@...ras.ru>
> 
> ---
> diff --git a/./a/drivers/scsi/scsi_lib.c b/./b/drivers/scsi/scsi_lib.c
> index f3c4089..a8f8e2f 100644
> --- a/./a/drivers/scsi/scsi_lib.c
> +++ b/./b/drivers/scsi/scsi_lib.c
> @@ -353,9 +353,9 @@ static void scsi_single_lun_run(struct scsi_device 
> *current_sdev)
>  
>  		spin_unlock_irqrestore(shost->host_lock, flags);
>  		blk_run_queue(sdev->request_queue);
> -		spin_lock_irqsave(shost->host_lock, flags);
>  	
> -		scsi_device_put(sdev);
> +		scsi_device_put(sdev);	
> +		spin_lock_irqsave(shost->host_lock, flags);
>  	}
>   out:
>  	spin_unlock_irqrestore(shost->host_lock, flags);
> 

Well this is strange.  afacit all the code to which you refer is
ancient, so why did this bug just pop up now?


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