lkml.org 
[lkml]   [2019]   [Aug]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Date
Subject[PATCH 3.16 020/157] NFS: fix mount/umount race in nlmclnt.
3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: NeilBrown <neilb@suse.com>

commit 4a9be28c45bf02fa0436808bb6c0baeba30e120e upstream.

If the last NFSv3 unmount from a given host races with a mount from the
same host, we can destroy an nlm_host that is still in use.

Specifically nlmclnt_lookup_host() can increment h_count on
an nlm_host that nlmclnt_release_host() has just successfully called
refcount_dec_and_test() on.
Once nlmclnt_lookup_host() drops the mutex, nlm_destroy_host_lock()
will be called to destroy the nlmclnt which is now in use again.

The cause of the problem is that the dec_and_test happens outside the
locked region. This is easily fixed by using
refcount_dec_and_mutex_lock().

Fixes: 8ea6ecc8b075 ("lockd: Create client-side nlm_host cache")
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
[bwh: Backported to 3.16: use atomic instead of refcount API]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/lockd/host.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--- a/fs/lockd/host.c
+++ b/fs/lockd/host.c
@@ -288,12 +288,11 @@ void nlmclnt_release_host(struct nlm_hos

WARN_ON_ONCE(host->h_server);

- if (atomic_dec_and_test(&host->h_count)) {
+ if (atomic_dec_and_mutex_lock(&host->h_count, &nlm_host_mutex)) {
WARN_ON_ONCE(!list_empty(&host->h_lockowners));
WARN_ON_ONCE(!list_empty(&host->h_granted));
WARN_ON_ONCE(!list_empty(&host->h_reclaim));

- mutex_lock(&nlm_host_mutex);
nlm_destroy_host_locked(host);
mutex_unlock(&nlm_host_mutex);
}
\
 
 \ /
  Last update: 2019-08-10 22:53    [W:0.421 / U:0.084 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site