Re: [Bug #11460] 2.6.27-rc3 to -rc4 regression: init 0 hangs in halt

Neil Brown
2008-09-01T02:54:57Z

On Saturday August 30, david-FQ/kcb21CSxWk0Htik3J/w@public.gmane.org wrote:
> Rafael J. Wysocki wrote:
> > This message has been generated automatically as a part of a report
> > of recent regressions.
> >
> > The following bug entry is on the current list of known regressions
> > from 2.6.26. Please verify if it still should be listed and let me know
> > (either way).
> >
> >
> > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=11460
> > Subject : 2.6.27-rc3 to -rc4 regression: init 0 hangs in halt
> > Submitter : David Greaves <david-FQ/kcb21CSxWk0Htik3J/w@public.gmane.org>
> > Date : 2008-08-30 04:07 (1 days old)
>
> Yes.
>
> I'm trying to bisect it but came across a bug/problem in git doing bisects.
> (see message subject "setlocalversion wasn't producing git labels for bisect")

Hi David.

Could you please try this patch?

Thanks,
NeilBrown

From 271f5a9b8f8ae0db95de72779d115c9d0b9d3cc5 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb-l3A5Bk7waGM@public.gmane.org>
Date: Mon, 1 Sep 2008 12:32:52 +1000
Subject: [PATCH] Remove invalidate_partition call from do_md_stop.

When stopping an md array, or just switching to read-only, we
currently call invalidate_partition while holding the mddev lock.
The main reason for this is probably to ensure all dirty buffers
are flushed (invalidate_partition calls fsync_bdev).

However if any dirty buffers are found, it will almost certainly cause
a deadlock as starting writeout will require an update to the
superblock, and performing that updates requires taking the mddev
lock - which is already held.

This deadlock can be demonstrated by running "reboot -f -n" with
a root filesystem on md/raid, and some dirty buffers in memory.

All other calls to stop an array should already happen after a flush.
The normal sequence is to stop using the array (e.g. umount) which
will cause __blkdev_put to call sync_blockdev. Then open the
array and issue the STOP_ARRAY ioctl while the buffers are all still
clean.

So this invalidate_partition is normally a no-op, except for one case
where it will cause a deadlock.

So remove it.

This patch possibly addresses the regression recored in
http://bugzilla.kernel.org/show_bug.cgi?id=11460
and
http://bugzilla.kernel.org/show_bug.cgi?id=11452

though it isn't yet clear how it ever worked.

Signed-off-by: NeilBrown <neilb-l3A5Bk7waGM@public.gmane.org>
---
drivers/md/md.c | 2 --
1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 8cfadc5..4790c83 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3841,8 +3841,6 @@ static int do_md_stop(mddev_t * mddev, int mode, int is_open)

del_timer_sync(&mddev->safemode_timer);

- invalidate_partition(disk, 0);
-
switch(mode) {
case 1: /* readonly */
err = -ENXIO;
--
1.5.6.5