NLM/lockd: Fix a race when cancelling a blocking lock
We shouldn't remove the lock from the list of blocked locks until the
CANCEL call has completed since we may be racing with a GRANTED callback.
Also ensure that we send an UNLOCK if the CANCEL request failed. Normally
that should only happen if the process gets hit with a fatal signal.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/lockd/clntproc.c b/fs/lockd/clntproc.c
index ea1a694..37d1aa2 100644
--- a/fs/lockd/clntproc.c
+++ b/fs/lockd/clntproc.c
@@ -510,6 +510,7 @@
struct nlm_res *resp = &req->a_res;
struct nlm_wait *block = NULL;
unsigned char fl_flags = fl->fl_flags;
+ unsigned char fl_type;
int status = -ENOLCK;
if (nsm_monitor(host) < 0) {
@@ -525,13 +526,16 @@
block = nlmclnt_prepare_block(host, fl);
again:
+ /*
+ * Initialise resp->status to a valid non-zero value,
+ * since 0 == nlm_lck_granted
+ */
+ resp->status = nlm_lck_blocked;
for(;;) {
/* Reboot protection */
fl->fl_u.nfs_fl.state = host->h_state;
status = nlmclnt_call(req, NLMPROC_LOCK);
if (status < 0)
- goto out_unblock;
- if (!req->a_args.block)
break;
/* Did a reclaimer thread notify us of a server reboot? */
if (resp->status == nlm_lck_denied_grace_period)
@@ -540,15 +544,22 @@
break;
/* Wait on an NLM blocking lock */
status = nlmclnt_block(block, req, NLMCLNT_POLL_TIMEOUT);
- /* if we were interrupted. Send a CANCEL request to the server
- * and exit
- */
if (status < 0)
- goto out_unblock;
+ break;
if (resp->status != nlm_lck_blocked)
break;
}
+ /* if we were interrupted while blocking, then cancel the lock request
+ * and exit
+ */
+ if (resp->status == nlm_lck_blocked) {
+ if (!req->a_args.block)
+ goto out_unlock;
+ if (nlmclnt_cancel(host, req->a_args.block, fl) == 0)
+ goto out_unblock;
+ }
+
if (resp->status == nlm_granted) {
down_read(&host->h_rwsem);
/* Check whether or not the server has rebooted */
@@ -562,16 +573,30 @@
printk(KERN_WARNING "%s: VFS is out of sync with lock manager!\n", __FUNCTION__);
up_read(&host->h_rwsem);
fl->fl_flags = fl_flags;
+ status = 0;
}
+ if (status < 0)
+ goto out_unlock;
status = nlm_stat_to_errno(resp->status);
out_unblock:
nlmclnt_finish_block(block);
- /* Cancel the blocked request if it is still pending */
- if (resp->status == nlm_lck_blocked)
- nlmclnt_cancel(host, req->a_args.block, fl);
out:
nlm_release_call(req);
return status;
+out_unlock:
+ /* Fatal error: ensure that we remove the lock altogether */
+ dprintk("lockd: lock attempt ended in fatal error.\n"
+ " Attempting to unlock.\n");
+ nlmclnt_finish_block(block);
+ fl_type = fl->fl_type;
+ fl->fl_type = F_UNLCK;
+ down_read(&host->h_rwsem);
+ do_vfs_lock(fl);
+ up_read(&host->h_rwsem);
+ fl->fl_type = fl_type;
+ fl->fl_flags = fl_flags;
+ nlmclnt_async_call(req, NLMPROC_UNLOCK, &nlmclnt_unlock_ops);
+ return status;
}
/*