| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.19 054/134] NFS: fix mount/umount race in nlmclnt. | Date | Mon, 1 Apr 2019 19:01:30 +0200 |
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4.19-stable 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") Cc: stable@vger.kernel.org (v2.6.38+) Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/lockd/host.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/fs/lockd/host.c +++ b/fs/lockd/host.c @@ -290,12 +290,11 @@ void nlmclnt_release_host(struct nlm_hos WARN_ON_ONCE(host->h_server); - if (refcount_dec_and_test(&host->h_count)) { + if (refcount_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); }
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