Possible-Patch: unregister bdi on error path.

Neil Brown
2010-03-10T22:13:42Z

Hi,
I've had an internal report of the following error:

[145405.949506] WARNING: at /usr/src/packages/BUILD/kernel-default-2.6.32.8/linux-2.6.32/fs/sysfs/dir.c:491 sysfs_add_one+0xf4/0x120()
[145405.949516] sysfs: cannot create duplicate filename '/devices/virtual/bdi/0:26'
...
[145405.949598] Pid: 8745, comm: mount.nfs Not tainted 2.6.32.8-0.3-default #1
[145405.949601] Call Trace:
...
[145405.949644] [<ffffffff811877c4>] sysfs_add_one+0xf4/0x120
[145405.949650] [<ffffffff811883c0>] create_dir+0x60/0xb0
[145405.949656] [<ffffffff81188441>] sysfs_create_dir+0x31/0x50
[145405.949663] [<ffffffff8120a8ef>] kobject_add_internal+0xff/0x260
[145405.949669] [<ffffffff8120ac56>] kobject_add+0x46/0x70
[145405.949675] [<ffffffff812c06b6>] device_add+0xc6/0x4e0
[145405.949682] [<ffffffff812c0c2f>] device_create_vargs+0x13f/0x150
[145405.949689] [<ffffffff810eceea>] bdi_register+0x7a/0x180
[145405.949707] [<ffffffffa04fb006>] nfs_get_sb+0x316/0x430 [nfs]
[145405.949735] [<ffffffff8112195d>] vfs_kern_mount+0x7d/0x1b0
[145405.949741] [<ffffffff81121af3>] do_kern_mount+0x53/0x120
[145405.949748] [<ffffffff8113b7dc>] do_mount+0x21c/0x250
[145405.949754] [<ffffffff8113b8d0>] sys_mount+0xc0/0xf0

i.e. it tried to bdi_register 0:26 while it was already registered.

Looking through the code, it seems that if nfs_get_sb calls
nfs_bdi_register, but then doesn't set ->s_root, then ->put_super
is not called (generic_shutdown_super only calls ->put_super if s_root
is set), so the bdi is never unregistered. The next mount
would then trigger the above error.

I haven't found a way to trigger this situation, but it seems like it
should be possible.

Does this patch make sense?

Thanks,
NeilBrown

----------------------------
NFS: ensure bdi_unregister is called on mount failure.

bdi_unregister is called by nfs_put_super which is only called by
generic_shutdown_super if ->s_root is not NULL. So if we error out
in a circumstance where we called nfs_bdi_register (i.e. server !=
NULL) but have not set s_root, then we need to call bdi_unregister
explicitly in nfs_get_sb.

Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index f1afee4..da11ec9 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -2214,7 +2214,7 @@ static int nfs_get_sb(struct file_system_type *fs_type,
} else {
error = nfs_bdi_register(server);
if (error)
- goto error_splat_super;
+ goto error_splat_bdi;
}

if (!s->s_root) {
@@ -2256,6 +2256,9 @@ out_err_nosb:
error_splat_root:
dput(mntroot);
error_splat_super:
+ if (server && !s->s_root)
+ bdi_unregister(&server->backing_dev_info);
+error_splat_bdi:
deactivate_locked_super(s);
goto out;
}