On Thu, 2011-12-22 at 18:27 +0000, James Bottomley wrote:
> On Thu, 2011-12-22 at 11:10 +0800, Shaohua Li wrote:
> > scsi_run_queue() picks off all sdev from host starved_list to a local list,
> > then handle them. If there are multiple threads running scsi_run_queue(),
> > the starved_list will get messed. This is quite common, because request
> > rq_affinity is on by default.
> >
> > Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
> > ---
> > drivers/scsi/scsi_lib.c | 21 ++++++++++++++-------
> > 1 file changed, 14 insertions(+), 7 deletions(-)
> >
> > Index: linux/drivers/scsi/scsi_lib.c
> > ===================================================================
> > --- linux.orig/drivers/scsi/scsi_lib.c 2011-12-21 16:56:23.000000000 +0800
> > +++ linux/drivers/scsi/scsi_lib.c 2011-12-22 09:33:09.000000000 +0800
> > @@ -401,9 +401,8 @@ static inline int scsi_host_is_busy(stru
> > */
> > static void scsi_run_queue(struct request_queue *q)
> > {
> > - struct scsi_device *sdev = q->queuedata;
> > + struct scsi_device *sdev = q->queuedata, *head_sdev = NULL;
> > struct Scsi_Host *shost;
> > - LIST_HEAD(starved_list);
> > unsigned long flags;
> >
> > /* if the device is dead, sdev will be NULL, so no queue to run */
> > @@ -415,9 +414,8 @@ static void scsi_run_queue(struct reques
> > scsi_single_lun_run(sdev);
> >
> > spin_lock_irqsave(shost->host_lock, flags);
> > - list_splice_init(&shost->starved_list, &starved_list);
> >
> > - while (!list_empty(&starved_list)) {
> > + while (!list_empty(&shost->starved_list)) {
>
> The original reason for working from a copy instead of the original list
> was that the device can end up back on the starved list because of a
> variety of conditions in the HBA and so this would cause the loop not to
> exit, so this piece of the patch doesn't look right to me.
+ /*
+ * the head sdev is no longer starved and removed from the
+ * starved list, select a new sdev as head.
+ */
+ if (head_sdev == sdev && list_empty(&sdev->starved_entry))
+ head_sdev = NULL;
I had this in the loop, which is to guarantee the loop will exit if a
device is removed from the starved list.
Thanks,
Shaohua
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