My patch should also fix your issue too, please see explanation in reply
to your patch. Do your testing show that it doesn't?
Thanks, Pavel.
On 11/21/2017 09:10 AM, Stuart Hayes wrote:
Pavel,
It turns out that the error handler on our systems was not getting woken up for
a different reason... I submitted a patch earlier today that fixes the issue I
were seeing (I CCed you on the patch).
Before I got my hands on the failing system and was able to root cause it, I
was pretty sure that your patch was going to fix our issue, because after I
examined the code paths, I couldn't find any other reason that the error
handler would not get woken up. I tried forcing the bug that your patch fixes
to occur, by compiling in some mdelay()s in a key place or two in the scsi
code, but it never failed for me that way. With my patch, several systems that
previously failed in 10 minutes or less successfully ran for many days.
Thanks,
Stuart
On 11/9/2017 8:54 AM, Pavel Tikhomirov wrote:
Are there any issues with this patch
(https://patchwork.kernel.org/patch/9938919/) that Pavel Tikhomirov submitted
back in September? I am willing to help if there's anything I can do to help
get it accepted.
Hi, Stuart, I asked James Bottomley about the patch status offlist and it seems
that the problem is - patch lacks testing and review. I would highly appreciate
review from your side and anyone who wants to participate!
And if you can confirm that the patch solves the problem on your environment with no side
effects please add "Tested-by:" tag also.
Thanks, Pavel
On 09/05/2017 03:54 PM, Pavel Tikhomirov wrote:
We have a problem on several our nodes with scsi EH. Imagine such an
order of execution of two threads:
CPU1 scsi_eh_scmd_add CPU2 scsi_host_queue_ready
/* shost->host_busy == 1 initialy */
if (shost->shost_state == SHOST_RECOVERY)
/* does not get here */
return 0;
lock(shost->host_lock);
shost->shost_state = SHOST_RECOVERY;
busy = shost->host_busy++;
/* host->can_queue == 1 initialy, busy == 1
* - go to starved label */
lock(shost->host_lock) /* wait */
shost->host_failed++;
/* shost->host_busy == 2, shost->host_failed == 1 */
call scsi_eh_wakeup(shost) {
if (host_busy == host_failed) {
/* does not get here */
wake_up_process(shost->ehandler)
}
}
unlock(shost->host_lock)
/* acquire lock */
shost->host_busy--;
Finaly we do not wakeup scsi_error_handler and all other commands
coming will hang as we are in never ending recovery state as there
is no one left to wakeup handler.
So scsi disc in these host becomes unresponsive and all bio on node
hangs. (We trigger these problem when scsi cmnds to DVD drive timeout.)
Main idea of the fix is to try to do wake up every time we decrement
host_busy or increment host_failed(the latter is already OK).
Now the very *last* one of busy threads getting host_lock after
decrementing host_busy will see all write operations on host's
shost_state, host_busy and host_failed completed thanks to implied
memory barriers on spin_lock/unlock, so at the time of busy==failed
we will trigger wakeup in at least one thread. (Thats why putting
recovery and failed checks under lock)
Signed-off-by: Pavel Tikhomirov <ptikhomi...@virtuozzo.com>
---
drivers/scsi/scsi_lib.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index f6097b89d5d3..6c99221d60aa 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -320,12 +320,11 @@ void scsi_device_unbusy(struct scsi_device *sdev)
if (starget->can_queue > 0)
atomic_dec(&starget->target_busy);
+ spin_lock_irqsave(shost->host_lock, flags);
if (unlikely(scsi_host_in_recovery(shost) &&
- (shost->host_failed || shost->host_eh_scheduled))) {
- spin_lock_irqsave(shost->host_lock, flags);
+ (shost->host_failed || shost->host_eh_scheduled)))
scsi_eh_wakeup(shost);
- spin_unlock_irqrestore(shost->host_lock, flags);
- }
+ spin_unlock_irqrestore(shost->host_lock, flags);
atomic_dec(&sdev->device_busy);
}
@@ -1503,6 +1502,13 @@ static inline int scsi_host_queue_ready(struct
request_queue *q,
spin_unlock_irq(shost->host_lock);
out_dec:
atomic_dec(&shost->host_busy);
+
+ spin_lock_irq(shost->host_lock);
+ if (unlikely(scsi_host_in_recovery(shost) &&
+ (shost->host_failed || shost->host_eh_scheduled)))
+ scsi_eh_wakeup(shost);
+ spin_unlock_irq(shost->host_lock);
+
return 0;
}
@@ -1964,6 +1970,13 @@ static blk_status_t scsi_queue_rq(struct
blk_mq_hw_ctx *hctx,
out_dec_host_busy:
atomic_dec(&shost->host_busy);
+
+ spin_lock_irq(shost->host_lock);
+ if (unlikely(scsi_host_in_recovery(shost) &&
+ (shost->host_failed || shost->host_eh_scheduled)))
+ scsi_eh_wakeup(shost);
+ spin_unlock_irq(shost->host_lock);
+
out_dec_target_busy:
if (scsi_target(sdev)->can_queue > 0)
atomic_dec(&scsi_target(sdev)->target_busy);
---
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