On Tue, Jul 28, 2009 at 12:18:14PM -0400, bfields wrote:
> On Mon, Jul 27, 2009 at 10:49:03PM +0100, Daniel J Blueman wrote:
> > After two days uptime on my NFS4 server with 2.6.31-rc4 and a few
> > 2.6.28 clients, I hit the file write-count
> > WARN_ON(f->f_mnt_write_state != 0) in file_take_write() in the
> > nfsd4_open path [1].
>
> Hm, so probably introduced by:
>
> e518f0560a191269bd345178c899c790eb1ad4c8 "nfsd: take file and mnt write
> in nfs4_upgrade_open".
>
> The other possible file_take_write() caller here is dentry_open (which
> calls it in the (f->f_mode & FMODE_WRITE) case).
>
> Looks like nfs4_upgrade_open() isn't handling error case cleanup
> correctly. Perhaps that could explain this.
The below (untested) should fix the error handling, at the expense of
making nfs4_upgrade_open() just a little more byzantine.
There's another problem, though: if our server gets a sequence like:
- OPEN for read
- OPEN for write
- OPEN_DOWNGRADE to read
- OPEN for write
all with the same open owner and file, then at the vfs level we do all
this with a single filp, like:
- OPEN for read
dentry_open();
- OPEN for write
get_write_access(inode);
mnt_want_write(mnt);
file_take_write(file);
- OPEN_DOWNGRADE to read
put_write_access(inode);
mnt_drop_write(mnt);
file_release_write(file);
- OPEN for write
get_write_access(inode);
mnt_want_write(mnt);
file_take_write(file);
But examination of the code shows that file_take_write() doesn't allow
this kind of use: you'll hit the warning you found, because
f_mnt_write_state == FILE_MNT_WRITE_TAKEN | FILE_MNT_WRITE_RELEASE;
We could fix that by replacing our file_release_write() with a
file_reset_write(). But I suspect we're abusing the VFS interface, and
we should really just keep separate filp's for read and write.
--b.
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 7729d09..3018839 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2378,14 +2378,19 @@ nfs4_upgrade_open(struct svc_rqst *rqstp, struct svc_fh *cur_fh, struct nfs4_sta
if (err)
return nfserrno(err);
err = mnt_want_write(cur_fh->fh_export->ex_path.mnt);
- if (err)
+ if (err) {
+ put_write_access(inode);
return nfserrno(err);
+ }
file_take_write(filp);
}
status = nfsd4_truncate(rqstp, cur_fh, open);
if (status) {
- if (new_writer)
+ if (new_writer) {
+ file_reset_write(filp);
+ mnt_drop_write(cur_fh->fh_export->ex_path.mnt);
put_write_access(inode);
+ }
return status;
}
/* remember the open */
--
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