[PATCH] rbd: prevent busy loop when requesting exclusive lock

[Ilya Dryomov <idryomov@gmail.com>]

Due to rbd_try_acquire_lock() effectively swallowing all but
EBLOCKLISTED error from rbd_try_lock() ("request lock anyway") and
rbd_request_lock() returning ETIMEDOUT error not only for an actual
notify timeout but also when the lock owner doesn't respond, a busy
loop inside of rbd_acquire_lock() between rbd_try_acquire_lock() and
rbd_request_lock() is possible.

Requesting the lock on EBUSY error (returned by get_lock_owner_info()
if an incompatible lock or invalid lock owner is detected) makes very
little sense.  The same goes for ETIMEDOUT error (might pop up pretty
much anywhere if osd_request_timeout option is set) and many others.

Just fail I/O requests on rbd_dev->acquiring_list immediately on any
error from rbd_try_lock().

Cc: stable@vger.kernel.org # 588159009d5b: rbd: retrieve and check lock owner twice before blocklisting
Cc: stable@vger.kernel.org
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 drivers/block/rbd.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 24afcc93ac01..2328cc05be36 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -3675,7 +3675,7 @@ static int rbd_lock(struct rbd_device *rbd_dev)
 	ret = ceph_cls_lock(osdc, &rbd_dev->header_oid, &rbd_dev->header_oloc,
 			    RBD_LOCK_NAME, CEPH_CLS_LOCK_EXCLUSIVE, cookie,
 			    RBD_LOCK_TAG, "", 0);
-	if (ret)
+	if (ret && ret != -EEXIST)
 		return ret;
 
 	__rbd_lock(rbd_dev, cookie);
@@ -3878,7 +3878,7 @@ static struct ceph_locker *get_lock_owner_info(struct rbd_device *rbd_dev)
 				 &rbd_dev->header_oloc, RBD_LOCK_NAME,
 				 &lock_type, &lock_tag, &lockers, &num_lockers);
 	if (ret) {
-		rbd_warn(rbd_dev, "failed to retrieve lockers: %d", ret);
+		rbd_warn(rbd_dev, "failed to get header lockers: %d", ret);
 		return ERR_PTR(ret);
 	}
 
@@ -3940,8 +3940,10 @@ static int find_watcher(struct rbd_device *rbd_dev,
 	ret = ceph_osdc_list_watchers(osdc, &rbd_dev->header_oid,
 				      &rbd_dev->header_oloc, &watchers,
 				      &num_watchers);
-	if (ret)
+	if (ret) {
+		rbd_warn(rbd_dev, "failed to get watchers: %d", ret);
 		return ret;
+	}
 
 	sscanf(locker->id.cookie, RBD_LOCK_COOKIE_PREFIX " %llu", &cookie);
 	for (i = 0; i < num_watchers; i++) {
@@ -3985,8 +3987,12 @@ static int rbd_try_lock(struct rbd_device *rbd_dev)
 		locker = refreshed_locker = NULL;
 
 		ret = rbd_lock(rbd_dev);
-		if (ret != -EBUSY)
+		if (!ret)
+			goto out;
+		if (ret != -EBUSY) {
+			rbd_warn(rbd_dev, "failed to lock header: %d", ret);
 			goto out;
+		}
 
 		/* determine if the current lock holder is still alive */
 		locker = get_lock_owner_info(rbd_dev);
@@ -4089,11 +4095,8 @@ static int rbd_try_acquire_lock(struct rbd_device *rbd_dev)
 
 	ret = rbd_try_lock(rbd_dev);
 	if (ret < 0) {
-		rbd_warn(rbd_dev, "failed to lock header: %d", ret);
-		if (ret == -EBLOCKLISTED)
-			goto out;
-
-		ret = 1; /* request lock anyway */
+		rbd_warn(rbd_dev, "failed to acquire lock: %d", ret);
+		goto out;
 	}
 	if (ret > 0) {
 		up_write(&rbd_dev->lock_rwsem);
@@ -6627,12 +6630,11 @@ static int rbd_add_acquire_lock(struct rbd_device *rbd_dev)
 		cancel_delayed_work_sync(&rbd_dev->lock_dwork);
 		if (!ret)
 			ret = -ETIMEDOUT;
-	}
 
-	if (ret) {
-		rbd_warn(rbd_dev, "failed to acquire exclusive lock: %ld", ret);
-		return ret;
+		rbd_warn(rbd_dev, "failed to acquire lock: %ld", ret);
 	}
+	if (ret)
+		return ret;
 
 	/*
 	 * The lock may have been released by now, unless automatic lock
-- 
2.41.0