Re: [PATCH] scsi_lib.c: sleeping function called from invalidcontext

From: Andrew Morton
Date: Thu Sep 24 2009 - 18:57:45 EST


On Wed, 23 Sep 2009 17:58:47 +0000
iceberg <strakh@xxxxxxxxx> 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@xxxxxxxxx>
>
> ---
> 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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