Patchwork block: Prevent hang_check firing during long I/O

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Submitter Mark Lord
Date Sept. 24, 2010, 1:51 p.m.
Message ID <1285336273.9259.2.camel@corey>
Download mbox | patch
Permalink /patch/65652/
State Not Applicable
Delegated to: David Miller
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Comments

Mark Lord - Sept. 24, 2010, 1:51 p.m.
During long I/O operations, the hang_check timer may fire,
trigger stack dumps that unnecessarily alarm the user.

Eg.  hdparm --security-erase NULL /dev/sdb  ## can take *hours* to complete

So, if hang_check is armed, we should wake up periodically
to prevent it from triggering.  This patch uses a wake-up interval
equal to half the hang_check timer period, which keeps overhead low enough.

Signed-off-by: Mark Lord <mlord@pobox.com>



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Jens Axboe - Sept. 24, 2010, 1:52 p.m.
On 2010-09-24 15:51, Mark Lord wrote:
> During long I/O operations, the hang_check timer may fire,
> trigger stack dumps that unnecessarily alarm the user.
> 
> Eg.  hdparm --security-erase NULL /dev/sdb  ## can take *hours* to complete
> 
> So, if hang_check is armed, we should wake up periodically
> to prevent it from triggering.  This patch uses a wake-up interval
> equal to half the hang_check timer period, which keeps overhead low enough.

Applied, thanks.

Patch

--- old/block/blk-exec.c	2010-09-20 19:56:53.000000000 -0400
+++ linux/block/blk-exec.c	2010-09-24 09:43:32.342604574 -0400
@@ -80,6 +80,7 @@ 
 	DECLARE_COMPLETION_ONSTACK(wait);
 	char sense[SCSI_SENSE_BUFFERSIZE];
 	int err = 0;
+	unsigned long hang_check;
 
 	/*
 	 * we need an extra reference to the request, so we can look at
@@ -95,7 +96,13 @@ 
 
 	rq->end_io_data = &wait;
 	blk_execute_rq_nowait(q, bd_disk, rq, at_head, blk_end_sync_rq);
-	wait_for_completion(&wait);
+
+	/* Prevent hang_check timer from firing at us during very long I/O */
+	hang_check = sysctl_hung_task_timeout_secs;
+	if (hang_check)
+		while (!wait_for_completion_timeout(&wait, hang_check * (HZ/2)));
+	else
+		wait_for_completion(&wait);
 
 	if (rq->errors)
 		err = -EIO;