Hi,
On 08/12/11 00:16, Alan Stern wrote:
> On Thu, 11 Aug 2011, James Bottomley wrote:
>> However, much as I'd like to accept this rosy view, the original oops
>> that started all of this in 2.6.38 was someone caught something with a
>> reference to a SCSI queue after the device release function had been
>> called.
>
> Not according to your commit log. You wrote that the reference was
> taken after scsi_remove_device() had been called -- but the device
> release function is scsi_device_dev_release_usercontext().
The commit log of 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b
("[SCSI] put stricter guards on queue dead checks") does not
explain about the move of scsi_free_queue().
But according to the discussion below, it seems
the move was motivated to solve the following self-deadlock:
https://lkml.org/lkml/2011/4/12/9
[in the context of kblockd_workqueue]
blk_delay_work
__blk_run_queue
scsi_request_fn
put_device
(puts final sdev refcount)
scsi_device_dev_release
execute_in_process_context(scsi_device_dev_release_usercontext)
[execute immediately because it's in process context]
scsi_device_dev_release_usercontext
scsi_free_queue
blk_cleanup_queue
blk_sync_queue
(wait for blk_delay_work to complete...)
James, is my understanding correct?
If so, isn't it possible to move the scsi_free_queue back to
the original place and solve the deadlock instead by
avoiding the wait in the same context?
@@ -338,8 +339,8 @@ static void scsi_device_dev_release_user
static void scsi_device_dev_release(struct device *dev)
{
struct scsi_device *sdp = to_scsi_device(dev);
- execute_in_process_context(scsi_device_dev_release_usercontext,
- &sdp->ew);
+ INIT_WORK(&sdp->ew.work, scsi_device_dev_release_usercontext);
+ schedule_work(&sdp->ew.work);
}
static struct class sdev_class = {
Thanks,
--
Jun'ichi Nomura, NEC Corporation
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