If there are some mount points(not exported for nfs) under
a pseudo root, after client's operation of those entry under
the root, anyone can unmount those mount points until nfsd stop.
# cat /etc/exports
/nfs/xfs *(rw,insecure,no_subtree_check,no_root_squash)
/nfs/pnfs *(rw,insecure,no_subtree_check,no_root_squash)
# ll /nfs/
total 0
drwxr-xr-x. 3 root root 84 Apr 21 22:27 pnfs
drwxr-xr-x. 3 root root 84 Apr 21 22:27 test
drwxr-xr-x. 2 root root 6 Apr 20 22:01 xfs
# mount /dev/sde /nfs/test
# df
Filesystem 1K-blocks Used Available Use% Mounted on
......
/dev/sdd 1038336 32944 1005392 4% /nfs/pnfs
/dev/sdc 10475520 32928 10442592 1% /nfs/xfs
/dev/sde 999320 1284 929224 1% /nfs/test
# mount -t nfs 127.0.0.1:/nfs/ /mnt
# ll /mnt/*/
/mnt/pnfs/:
total 0
-rw-r--r--. 1 root root 0 Apr 21 22:23 attr
drwxr-xr-x. 2 root root 6 Apr 21 22:19 tmp
/mnt/xfs/:
total 0
# umount /nfs/test/
umount: /nfs/test/: target is busy
(In some cases useful info about processes that
use the device is found by lsof(8) or fuser(1).)
I don't think that's user expect, they want umount /nfs/test/.
It's caused by exports cache of nfsd holds the reference of
the path (here is /nfs/test/), so, it can't umounted until nfsd stop.
There is one strange thing exist, the export cache status of
/nfs/test/ is CACHE_NEGATIVE, also hold the reference of the path.
I think nfsd should not hold the reference when CACHE_NEGATIVE.
I can't find a better way to put the reference, just path it after
svc_export_update().
Any comments are welcome, thanks.
Signed-off-by: Kinglong Mee <kinglongmee@xxxxxxxxx>
---
fs/nfsd/export.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index c3e3b6e..5595cffc7 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -793,9 +793,15 @@ svc_export_update(struct svc_export *new, struct svc_export *old)
int hash = svc_export_hash(old);
ch = sunrpc_cache_update(old->cd, &new->h, &old->h, hash);
- if (ch)
- return container_of(ch, struct svc_export, h);
- else
+ if (ch) {
+ struct svc_export *exp = container_of(ch, struct svc_export, h);
+ if (test_bit(CACHE_NEGATIVE, &exp->h.flags)) {
+ path_put(&exp->ex_path);
+ exp->ex_path.mnt = NULL;
+ exp->ex_path.dentry = NULL;
+ }
+ return exp;
+ } else
return NULL;
}
--
2.3.5
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