Re: [PATCH 4/4] scsi: Stop accepting SCSI requests before removing a device

[Bart Van Assche <bvanassche@acm.org>]

On 06/05/12 22:08, Mike Christie wrote:

> On 06/05/2012 12:14 PM, Bart Van Assche wrote:
>> Avoid that the code for requeueing SCSI requests triggers a
>> crash by making sure that that code isn't scheduled anymore
>> after a device has been removed.
>>
>> Also, source code inspection of __scsi_remove_device() revealed
>> a race condition in this function: no new SCSI requests must be
>> accepted for a SCSI device after device removal started.
>>
>> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
>> Cc: Mike Christie <michaelc@cs.wisc.edu>
>> Cc: James Bottomley <JBottomley@parallels.com>
>> Cc: Jens Axboe <axboe@kernel.dk>
>> Cc: Joe Lawrence <jdl1291@gmail.com>
>> Cc: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
>> Cc: <stable@kernel.org>
>> ---
>>  drivers/scsi/scsi_lib.c   |    7 ++++---
>>  drivers/scsi/scsi_sysfs.c |   11 +++++++++--
>>  2 files changed, 13 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index 082c1e5..b722a8b 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -158,10 +158,11 @@ static void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
>>  	 * that are already in the queue.
>>  	 */
>>  	spin_lock_irqsave(q->queue_lock, flags);
>> -	blk_requeue_request(q, cmd->request);
>> +	if (!blk_queue_dead(q)) {
>> +		blk_requeue_request(q, cmd->request);
>> +		kblockd_schedule_work(q, &device->requeue_work);
>> +	}
>>  	spin_unlock_irqrestore(q->queue_lock, flags);
>> -
>> -	kblockd_schedule_work(q, &device->requeue_work);
> 
> If we do not have the part of the patch above, but have your other
> patches and the code below, will we be ok?


I'm not sure. Without the above part the request could get killed after
the blk_requeue_request() call finished but before the requeue_work is
scheduled, e.g. because the request timer fired or due to a
blk_abort_queue() call.

Bart.