linux-kernel - Re: XFS related Oops (suspend/resume related)

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Message-Id: <200711292205.25431.rjw@sisk.pl>
Date:	Thu, 29 Nov 2007 22:05:24 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Tino Keitel <tino.keitel@....de>
Cc:	David Chinner <dgc@....com>, linux-kernel@...r.kernel.org,
	xfs@....sgi.com
Subject: Re: XFS related Oops (suspend/resume related)

On Tuesday, 27 of November 2007, Rafael J. Wysocki wrote:
> On Tuesday, 27 of November 2007, David Chinner wrote:
> > On Tue, Nov 27, 2007 at 04:51:38PM +0100, Rafael J. Wysocki wrote:
> > > On Monday, 26 of November 2007, Rafael J. Wysocki wrote:
> > > > On Monday, 26 of November 2007, David Chinner wrote:
> > > > > Now there's a message that I haven't seen in about 3 years.
> > > > > 
> > > > > It indicates that the linux inode connected to the xfs_inode is not
> > > > > the correct one. i.e. that the linux inode cache is out of step with
> > > > > the XFS inode cache.
> > > > > 
> > > > > Basically, that is not supposed to happen. I suspect that the way
> > > > > threads are frozen is resulting in an inode lookup racing with
> > > > > a reclaim. The reclaim thread gets stopped after any use threads,
> > > > > and so we could have the situation that a process blocked in lookup
> > > > > has the XFS inode reclaimed and reused before it gets unblocked.
> > > > > 
> > > > > The question is why is it happening now when none of that code in
> > > > > XFS has changed?
> > > > > 
> > > > > Rafael, when are threads frozen? Only when they schedule or call
> > > > > try_to_freeze()?
> > > > 
> > > > Kernel threads freeze only when they call try_to_freeze().  User space tasks
> > > > freeze while executing the signals handling code.
> > > > 
> > > > > Did the freezer mechanism change in 2.6.23 (this is on 2.6.23.1)?
> > > > 
> > > > Yes.  Kernel threads are not sent fake signals by the freezer any more.
> > > 
> > > Ah, sorry, this change has been merged after 2.6.23.  However, before 2.6.23
> > > we had another important change that caused all kernel threads to have
> > > PF_NOFREEZE set by default, unless they call set_freezable() explicitly.
> > 
> > So try_to_freeze() will never freeze a thread if it has not been
> > set_freezable()? And xfsbufd will never be frozen?
> 
> No, it won't.
> 
> I must have overlooked it, probably because it calls refrigerator() directly
> and not try_to_freeze() ...
> 
> I think something like the appended patch will help, then.

Tino, can you check if this patch helps, please?

Greetings,
Rafael


> ---
> Fix breakage caused by commit 831441862956fffa17b9801db37e6ea1650b0f69
> that did not introduce the necessary call to set_freezable() in
> xfs/linux-2.6/xfs_buf.c .
> 
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> ---
>  fs/xfs/linux-2.6/xfs_buf.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> Index: linux-2.6/fs/xfs/linux-2.6/xfs_buf.c
> ===================================================================
> --- linux-2.6.orig/fs/xfs/linux-2.6/xfs_buf.c
> +++ linux-2.6/fs/xfs/linux-2.6/xfs_buf.c
> @@ -1750,6 +1750,8 @@ xfsbufd(
>  
>  	current->flags |= PF_MEMALLOC;
>  
> +	set_freezable();
> +
>  	do {
>  		if (unlikely(freezing(current))) {
>  			set_bit(XBT_FORCE_SLEEP, &target->bt_flags);
> -
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> 



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