linux-ext4 - Re: warning in ext4_journal_start

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Date:	Mon, 24 Feb 2014 10:45:32 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Jan Kara <jack@...e.cz>
Cc:	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, 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?

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.

--b.

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);
--
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