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: [email protected] (v2.6.38+)
Signed-off-by: NeilBrown <[email protected]>
---
fs/lockd/host.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/fs/lockd/host.c b/fs/lockd/host.c
index 93fb7cf0b92b..f0b5c987d6ae 100644
--- a/fs/lockd/host.c
+++ b/fs/lockd/host.c
@@ -290,12 +290,11 @@ void nlmclnt_release_host(struct nlm_host *host)
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);
}
--
2.14.0.rc0.dirty
On Tue, 2019-03-19 at 11:33 +1100, NeilBrown wrote:
> 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: [email protected] (v2.6.38+)
> Signed-off-by: NeilBrown <[email protected]>
> ---
> fs/lockd/host.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/fs/lockd/host.c b/fs/lockd/host.c
> index 93fb7cf0b92b..f0b5c987d6ae 100644
> --- a/fs/lockd/host.c
> +++ b/fs/lockd/host.c
> @@ -290,12 +290,11 @@ void nlmclnt_release_host(struct nlm_host
> *host)
>
> 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);
> }
Thanks Neil! Applying to linux-next.
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
[email protected]