[PATCH] NLM: fix a client-side race on blocking locks.

 If the lock blocks, the server may send us a GRANTED message that
 races with the reply to our LOCK request. Make sure that we catch
 the GRANTED by queueing up our request on the nlm_blocked list
 before we send off the first LOCK rpc call.

 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 90 insertions, 49 deletions

diff --git a/fs/lockd/clntlock.c b/fs/lockd/clntlock.c
index 44adb84183b6..006bb9e14579 100644
--- a/fs/lockd/clntlock.c
+++ b/fs/lockd/clntlock.c
@@ -42,23 +42,51 @@ struct nlm_wait {
 static LIST_HEAD(nlm_blocked);
 
 /*
- * Block on a lock
+ * Queue up a lock for blocking so that the GRANTED request can see it
  */
-int
-nlmclnt_block(struct nlm_host *host, struct file_lock *fl, u32 *statp)
+int nlmclnt_prepare_block(struct nlm_rqst *req, struct nlm_host *host, struct file_lock *fl)
+{
+        struct nlm_wait *block;
+
+        BUG_ON(req->a_block != NULL);
+        block = kmalloc(sizeof(*block), GFP_KERNEL);
+        if (block == NULL)
+                return -ENOMEM;
+        block->b_host = host;
+        block->b_lock = fl;
+        init_waitqueue_head(&block->b_wait);
+        block->b_status = NLM_LCK_BLOCKED;
+
+        list_add(&block->b_list, &nlm_blocked);
+        req->a_block = block;
+
+        return 0;
+}
+
+void nlmclnt_finish_block(struct nlm_rqst *req)
 {
-        struct nlm_wait block, **head;
-        int             err;
-        u32             pstate;
+        struct nlm_wait *block = req->a_block;
 
-        block.b_host   = host;
-        block.b_lock   = fl;
-        init_waitqueue_head(&block.b_wait);
-        block.b_status = NLM_LCK_BLOCKED;
-        list_add(&block.b_list, &nlm_blocked);
+        if (block == NULL)
+                return;
+        req->a_block = NULL;
+        list_del(&block->b_list);
+        kfree(block);
+}
 
-        /* Remember pseudo nsm state */
-        pstate = host->h_state;
+/*
+ * Block on a lock
+ */
+long nlmclnt_block(struct nlm_rqst *req, long timeout)
+{
+        struct nlm_wait *block = req->a_block;
+        long ret;
+
+        /* A borken server might ask us to block even if we didn't
+         * request it. Just say no!
+         */
+        if (!req->a_args.block)
+                return -EAGAIN;
 
         /* Go to sleep waiting for GRANT callback. Some servers seem
          * to lose callbacks, however, so we're going to poll from
@@ -68,23 +96,16 @@ nlmclnt_block(struct nlm_host *host, struct file_lock *fl, u32 *statp)
          * a 1 minute timeout would do. See the comment before
          * nlmclnt_lock for an explanation.
          */
-        sleep_on_timeout(&block.b_wait, 30*HZ);
+        ret = wait_event_interruptible_timeout(block->b_wait,
+                        block->b_status != NLM_LCK_BLOCKED,
+                        timeout);
 
-        list_del(&block.b_list);
-
-        if (!signalled()) {
-                *statp = block.b_status;
-                return 0;
+        if (block->b_status != NLM_LCK_BLOCKED) {
+                req->a_res.status = block->b_status;
+                block->b_status = NLM_LCK_BLOCKED;
         }
 
-        /* Okay, we were interrupted. Cancel the pending request
-         * unless the server has rebooted.
-         */
-        if (pstate == host->h_state && (err = nlmclnt_cancel(host, fl)) < 0)
-                printk(KERN_NOTICE
-                        "lockd: CANCEL call failed (errno %d)\n", -err);
-
-        return -ERESTARTSYS;
+        return ret;
 }
 
 /*
@@ -94,27 +115,23 @@ u32
 nlmclnt_grant(struct nlm_lock *lock)
 {
         struct nlm_wait *block;
+        u32 res = nlm_lck_denied;
 
         /*
          * Look up blocked request based on arguments. 
          * Warning: must not use cookie to match it!
          */
         list_for_each_entry(block, &nlm_blocked, b_list) {
-                if (nlm_compare_locks(block->b_lock, &lock->fl))
-                        break;
+                if (nlm_compare_locks(block->b_lock, &lock->fl)) {
+                        /* Alright, we found a lock. Set the return status
+                         * and wake up the caller
+                         */
+                        block->b_status = NLM_LCK_GRANTED;
+                        wake_up(&block->b_wait);
+                        res = nlm_granted;
+                }
         }
-
-        /* Ooops, no blocked request found. */
-        if (block == NULL)
-                return nlm_lck_denied;
-
-        /* Alright, we found the lock. Set the return status and
-         * wake up the caller.
-         */
-        block->b_status = NLM_LCK_GRANTED;
-        wake_up(&block->b_wait);
-
-        return nlm_granted;
+        return res;
 }
 
 /*
diff --git a/fs/lockd/clntproc.c b/fs/lockd/clntproc.c
index a4407619b1f1..fd77ed1d710d 100644
--- a/fs/lockd/clntproc.c
+++ b/fs/lockd/clntproc.c
@@ -21,6 +21,7 @@
 
 #define NLMDBG_FACILITY         NLMDBG_CLIENT
 #define NLMCLNT_GRACE_WAIT      (5*HZ)
+#define NLMCLNT_POLL_TIMEOUT    (30*HZ)
 
 static int      nlmclnt_test(struct nlm_rqst *, struct file_lock *);
 static int      nlmclnt_lock(struct nlm_rqst *, struct file_lock *);
@@ -553,7 +554,8 @@ nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
 {
         struct nlm_host *host = req->a_host;
         struct nlm_res  *resp = &req->a_res;
-        int             status;
+        long timeout;
+        int status;
 
         if (!host->h_monitored && nsm_monitor(host) < 0) {
                 printk(KERN_NOTICE "lockd: failed to monitor %s\n",
@@ -562,15 +564,32 @@ nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
                 goto out;
         }
 
-        do {
-                if ((status = nlmclnt_call(req, NLMPROC_LOCK)) >= 0) {
-                        if (resp->status != NLM_LCK_BLOCKED)
-                                break;
-                        status = nlmclnt_block(host, fl, &resp->status);
-                }
+        if (req->a_args.block) {
+                status = nlmclnt_prepare_block(req, host, fl);
                 if (status < 0)
                         goto out;
-        } while (resp->status == NLM_LCK_BLOCKED && req->a_args.block);
+        }
+        for(;;) {
+                status = nlmclnt_call(req, NLMPROC_LOCK);
+                if (status < 0)
+                        goto out_unblock;
+                if (resp->status != NLM_LCK_BLOCKED)
+                        break;
+                /* Wait on an NLM blocking lock */
+                timeout = nlmclnt_block(req, NLMCLNT_POLL_TIMEOUT);
+                /* Did a reclaimer thread notify us of a server reboot? */
+                if (resp->status ==  NLM_LCK_DENIED_GRACE_PERIOD)
+                        continue;
+                if (resp->status != NLM_LCK_BLOCKED)
+                        break;
+                if (timeout >= 0)
+                        continue;
+                /* We were interrupted. Send a CANCEL request to the server
+                 * and exit
+                 */
+                status = (int)timeout;
+                goto out_unblock;
+        }
 
         if (resp->status == NLM_LCK_GRANTED) {
                 fl->fl_u.nfs_fl.state = host->h_state;
@@ -579,6 +598,11 @@ nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
                 do_vfs_lock(fl);
         }
         status = nlm_stat_to_errno(resp->status);
+out_unblock:
+        nlmclnt_finish_block(req);
+        /* Cancel the blocked request if it is still pending */
+        if (resp->status == NLM_LCK_BLOCKED)
+                nlmclnt_cancel(host, fl);
 out:
         nlmclnt_release_lockargs(req);
         return status;