linux-kernel - Re: next-20081119: general protection fault: get_next_timer

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Message-ID: <20081124213517.GA25898@linux.vnet.ibm.com>
Date:	Mon, 24 Nov 2008 13:35:17 -0800
From:	Mike Anderson <andmike@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Alexander Beregalov <a.beregalov@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-next@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, linux-scsi@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: next-20081119: general protection fault:
	get_next_timer_interrupt()

Thomas Gleixner <tglx@...utronix.de> wrote:
> > Well, not sure.  Most likely candidate is the new block timer code.
> > What seems to be happening is that the queue is being released with
> > either an outstanding request (refcounting problem) or ticking timer
> > with no work (block timer problem).  The way scanning works is that we
> > create a request queue for each device we probe and then delete it again
> > if nothing appears after the bus settle time.   The argument against
> > this is that it should show up on every scanned bus.  However, these are
> > getting rarer; I was just about to write that I hadn't seen it when I
> > remembered that all my SCSI testing systems are currently running
> > hotplug reporting busses (i.e. don't do scanning).  However,
> > fortunately, I've also booted voyager recently which does use parallel
> > SCSI and doesn't see this either, so it could also be megaraid_sas
> > specific.
> 
> Yeah, block could it be as well. Jens, Mike ?

I added a comment to bug 12020 on Thursday about a few other systems that
where seeing the signature shown in bug 12020. It appeared from debug that
there where a few paths that where adding timers for requests that where
not expected.

http://bugzilla.kernel.org/show_bug.cgi?id=12020

It would be good to know if the debug patch below effects your problem as while.

If it does we need to investigated a solution to resolve not adding a
timer for these requests.

-andmike
--
Michael Anderson
andmike@...ux.vnet.ibm.com



blk: blk_add_timer debug patch

[DEBUG] Debug only patch.

Debug patch to blk_add_timer to not start timer for request that do not
have the REQ_STARTED flag set.

Signed-off-by: Mike Anderson <andmike@...ux.vnet.ibm.com>
---
 block/blk-timeout.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index 69185ea..4389391 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -177,6 +177,9 @@ void blk_add_timer(struct request *req)
 	BUG_ON(!list_empty(&req->timeout_list));
 	BUG_ON(test_bit(REQ_ATOM_COMPLETE, &req->atomic_flags));
 
+	if (!(req->cmd_flags & REQ_STARTED))
+		return;
+
 	if (req->timeout)
 		req->deadline = jiffies + req->timeout;
 	else {
-- 
1.5.6.5

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