From: Stefano Stabellini Date: Wed, 15 Nov 2017 21:20:21 +0000 (-0800) Subject: xen/pvcalls: fix potential endless loop in pvcalls-front.c X-Git-Tag: v4.15-rc1~78^2 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=646d944c2ef5a3b298c4e150494c71b9272d8b47;p=linux-block.git xen/pvcalls: fix potential endless loop in pvcalls-front.c mutex_trylock() returns 1 if you take the lock and 0 if not. Assume you take in_mutex on the first try, but you can't take out_mutex. Next times you call mutex_trylock() in_mutex is going to fail. It's an endless loop. Solve the problem by waiting until the global refcount is 1 instead (the refcount is 1 when the only active pvcalls frontend function is pvcalls_front_release). Reported-by: Dan Carpenter Signed-off-by: Stefano Stabellini Signed-off-by: Boris Ostrovsky --- diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c index 9e40c2cd70b1..40caa92bff33 100644 --- a/drivers/xen/pvcalls-front.c +++ b/drivers/xen/pvcalls-front.c @@ -1041,13 +1041,12 @@ int pvcalls_front_release(struct socket *sock) wake_up_interruptible(&map->active.inflight_conn_req); /* - * Wait until there are no more waiters on the mutexes. - * We know that no new waiters can be added because sk_send_head - * is set to NULL -- we only need to wait for the existing - * waiters to return. + * We need to make sure that sendmsg/recvmsg on this socket have + * not started before we've cleared sk_send_head here. The + * easiest (though not optimal) way to guarantee this is to see + * that no pvcall (other than us) is in progress. */ - while (!mutex_trylock(&map->active.in_mutex) || - !mutex_trylock(&map->active.out_mutex)) + while (atomic_read(&pvcalls_refcount) > 1) cpu_relax(); pvcalls_front_free_map(bedata, map);