linux-ext4 - Re: warning in ext4_journal_start

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Message-ID: <20140225102126.GB1669@quack.suse.cz>
Date:	Tue, 25 Feb 2014 11:21:26 +0100
From:	Jan Kara <jack@...e.cz>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Jan Kara <jack@...e.cz>, Matthew Rahtz <mrahtz@...itasystems.com>,
	linux-ext4@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: warning in ext4_journal_start_sb on filesystem freeze

On Mon 24-02-14 10:45:32, J. Bruce Fields wrote:
> On Mon, Feb 24, 2014 at 10:55:25AM +0100, Jan Kara wrote:
> > On Sat 22-02-14 09:50:06, Matthew Rahtz wrote:
> > > Thanks for your help Jan,
> > > 
> > > A few months later, we've noticed the issue is actually still there.
> > > Using 3.11.0-17-generic on Ubuntu 12.04, we’re seeing this in the kernel
> > > logs:
> > > 
> > > [29243.606215] WARNING: CPU: 0 PID: 1785 at
> > > /build/buildd/linux-lts-saucy-3.11.0/fs/ext4/ext4_jbd2.c:48
> > > ext4_journal_check_start+0x83/0x90()
> > > 
> > > Having a look at the Ubuntu source package for that version, it
> > > definitely does include commit 03d95eb2f2578083a3f6286262e1cb5d88a00c02,
> > > and the line generating the warning is still:
> > > 
> > > WARN_ON(sb->s_writers.frozen == SB_FREEZE_COMPLETE);
> > > 
> > > Are there any other obvious possibilities for what may be causing this?
> > > There seem to be some users of Oracle Linux experiencing similar problems
> > > at https://community.oracle.com/thread/2617418, which was apparently
> > > fixed in Oracle's kernel version '3.8.13-26.el6uek'. Any word on when
> > > this might be integrated into the official kernel?
> > > 
> > > Full call trace included below.
> >   Looking at the trace below, now the problem seems to be in the NFS server
> > code. NFS should get protection against the filesystem being frozen (or
> > remounted read-only for that matter) via mnt_want_write() before calling
> > into notify_change() (actually before calling fh_lock() because of lock
> > ordering).  Similarly to what we do e.g. in fchownat(). Bruce?
> 
> Like this?
  Yup, that looks right.

> But I wonder why this is just popping up now--as far as I can tell we've
> had the bug since those write counts were introduced.
  Yeah, I'm wondering as well. NFS server on ext4 should have been
complaining for a long time.

								Honza

> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 6d7be3f..d573b61 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -445,12 +445,16 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
>  		err = nfserr_notsync;
>  		goto out_put_write_access;
>  	}
> +	host_err = fh_want_write(fhp);
> +	if (host_err)
> +		goto out_nfserr;
>  
>  	fh_lock(fhp);
>  	host_err = notify_change(dentry, iap, NULL);
>  	fh_unlock(fhp);
> +	fh_drop_write(fhp);
> +out_nfserr:
>  	err = nfserrno(host_err);
> -
>  out_put_write_access:
>  	if (size_change)
>  		put_write_access(inode);
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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