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NFS: fix mount/umount race in nlmclnt.
commit4a9be28c45
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:8ea6ecc8b0
("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>
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1 changed files with 1 additions and 2 deletions
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@ -290,12 +290,11 @@ void nlmclnt_release_host(struct nlm_host *host)
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WARN_ON_ONCE(host->h_server);
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if (refcount_dec_and_test(&host->h_count)) {
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if (refcount_dec_and_mutex_lock(&host->h_count, &nlm_host_mutex)) {
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WARN_ON_ONCE(!list_empty(&host->h_lockowners));
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WARN_ON_ONCE(!list_empty(&host->h_granted));
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WARN_ON_ONCE(!list_empty(&host->h_reclaim));
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mutex_lock(&nlm_host_mutex);
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nlm_destroy_host_locked(host);
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mutex_unlock(&nlm_host_mutex);
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}
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