On Sat, Mar 08, 2014 at 09:02:26AM +0000, Matthew Rahtz wrote: > Brilliant :) Thank you for your work! Just to make sure, have you been able to confirm yet that this eliminates the warning you were seeing? --b. > > ----- Original Message ----- > From: "J. Bruce Fields" <bfields@xxxxxxxxxxxx> > To: "Jan Kara" <jack@xxxxxxx> > Cc: "Matthew Rahtz" <mrahtz@xxxxxxxxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, linux-nfs@xxxxxxxxxxxxxxx > Sent: Tuesday, 4 March, 2014 7:04:42 PM > Subject: Re: warning in ext4_journal_start_sb on filesystem freeze > > On Tue, Mar 04, 2014 at 11:43:06AM -0500, J. Bruce Fields wrote: > > On Tue, Feb 25, 2014 at 11:21:26AM +0100, Jan Kara wrote: > > > 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. > > > > Ugh, actually, I didn't realize we can't do mnt_want_write recursively, > > and there's a confusing mixture of callers that do and don't already > > take it, so I'll have to do something a little more complicated. > > Actually it looks like there's an easy enough way to distinguish when we > need mnt_want_write and when we don't; hopefully the following does the > job. > > --b. > > commit b0f5cd115e811a146a6e1a4dd1e7cb85808cca23 > Author: J. Bruce Fields <bfields@xxxxxxxxxx> > Date: Mon Feb 24 14:59:47 2014 -0500 > > nfsd: notify_change needs elevated write count > > Looks like this bug has been here since these write counts were > introduced, not sure why it was just noticed now. > > Thanks also to Jan Kara for pointing out the problem. > > Reported-by: Matthew Rahtz <mrahtz@xxxxxxxxxxxxxxxxx> > Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx> > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > index 6d7be3f..eea5ad1 100644 > --- a/fs/nfsd/vfs.c > +++ b/fs/nfsd/vfs.c > @@ -404,6 +404,7 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap, > umode_t ftype = 0; > __be32 err; > int host_err; > + bool get_write_count; > int size_change = 0; > > if (iap->ia_valid & (ATTR_ATIME | ATTR_MTIME | ATTR_SIZE)) > @@ -411,10 +412,18 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap, > if (iap->ia_valid & ATTR_SIZE) > ftype = S_IFREG; > > + /* Callers that do fh_verify should do the fh_want_write: */ > + get_write_count = !fhp->fh_dentry; > + > /* Get inode */ > err = fh_verify(rqstp, fhp, ftype, accmode); > if (err) > goto out; > + if (get_write_count) { > + host_err = fh_want_write(fhp); > + if (host_err) > + return nfserrno(host_err); > + } > > dentry = fhp->fh_dentry; > inode = dentry->d_inode; > Please Note: Rapita Systems has a new address and telephone number. > Telephone: +44 1904 413945 > Address: Rapita Systems Ltd, Atlas House, > Osbaldwick Link Road, YORK, YO10 3JB > United Kingdom -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
