3.16.72-rc1 review patch. If anyone has any objections, please let me know.
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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); }