[dpdk-dev] [PATCH] ipc: fix locking while sending messages

[Anatoly Burakov]

Previously, we were putting an exclusive lock to prevent secondary
processes spinning up while we are sending our messages. However,
using exclusive locks had an effect of disallowing multiple
simultaenous unrelated messages/requests being sent, which was
not the intention behind locking.

Fix it to put a shared lock on the directory. That way, we still
prevent secondary process initializations while sending data over
IPC, but allow multiple unrelated transmissions to proceed.

Fixes: 89f1fe7e6d95 ("eal: lock IPC directory on init and send")
Cc: stable at dpdk.org

Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
---

Notes:
    This patch is needed for multiprocess hotplug support [1], to avoid cases
    where multiple requests deadlock while in progress.
    
    [1] http://patches.dpdk.org/project/dpdk/list/?series=252

 lib/librte_eal/common/eal_common_proc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_proc.c b/lib/librte_eal/common/eal_common_proc.c
index 707d8ab30..f010ef59e 100644
--- a/lib/librte_eal/common/eal_common_proc.c
+++ b/lib/librte_eal/common/eal_common_proc.c
@@ -786,7 +786,7 @@ mp_send(struct rte_mp_msg *msg, const char *peer, int type)
 
 	dir_fd = dirfd(mp_dir);
 	/* lock the directory to prevent processes spinning up while we send */
-	if (flock(dir_fd, LOCK_EX)) {
+	if (flock(dir_fd, LOCK_SH)) {
 		RTE_LOG(ERR, EAL, "Unable to lock directory %s\n",
 			mp_dir_path);
 		rte_errno = errno;
@@ -1020,7 +1020,7 @@ rte_mp_request_sync(struct rte_mp_msg *req, struct rte_mp_reply *reply,
 
 	dir_fd = dirfd(mp_dir);
 	/* lock the directory to prevent processes spinning up while we send */
-	if (flock(dir_fd, LOCK_EX)) {
+	if (flock(dir_fd, LOCK_SH)) {
 		RTE_LOG(ERR, EAL, "Unable to lock directory %s\n",
 			mp_dir_path);
 		closedir(mp_dir);
@@ -1146,7 +1146,7 @@ rte_mp_request_async(struct rte_mp_msg *req, const struct timespec *ts,
 	dir_fd = dirfd(mp_dir);
 
 	/* lock the directory to prevent processes spinning up while we send */
-	if (flock(dir_fd, LOCK_EX)) {
+	if (flock(dir_fd, LOCK_SH)) {
 		RTE_LOG(ERR, EAL, "Unable to lock directory %s\n",
 			mp_dir_path);
 		rte_errno = errno;
-- 
2.17.1