[dpdk-dev] [PATCH v2] eal: fix proc type auto detection

[Anatoly Burakov <anatoly.burakov@intel.com>]

Currently, primary process holds an exclusive lock on the config
file, thereby preventing other primaries from spinning up. However,
when the primary dies, the lock is no longer being held, even though
there might be other secondary processes still running.

The fix is two-fold. First of all, downgrade the primary process's
exclusive lock to a shared lock once we have it. Second of all,
also take out shared locks on the config from the secondaries. We
are using fcntl() locks, which get dropped when the file handle is
closed, so also remove the closure of config file handle.

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org

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

Notes:
    v2:
    - Adjusted indentation

 lib/librte_eal/linux/eal/eal.c | 37 +++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/lib/librte_eal/linux/eal/eal.c b/lib/librte_eal/linux/eal/eal.c
index 34db78753..0f0726703 100644
--- a/lib/librte_eal/linux/eal/eal.c
+++ b/lib/librte_eal/linux/eal/eal.c
@@ -83,6 +83,13 @@ static struct flock wr_lock = {
 		.l_len = sizeof(early_mem_config.memsegs),
 };
 
+static struct flock rd_lock = {
+	.l_type = F_RDLCK,
+	.l_whence = SEEK_SET,
+	.l_start = offsetof(struct rte_mem_config, memsegs),
+	.l_len = sizeof(early_mem_config.memsegs),
+};
+
 /* Address of global and public configuration */
 static struct rte_config rte_config = {
 		.mem_config = &early_mem_config,
@@ -343,8 +350,21 @@ rte_eal_config_create(void)
 	if (retval < 0){
 		close(mem_cfg_fd);
 		mem_cfg_fd = -1;
-		RTE_LOG(ERR, EAL, "Cannot create lock on '%s'. Is another primary "
-			"process running?\n", pathname);
+		RTE_LOG(ERR, EAL, "Cannot create exclusive lock on '%s'. "
+			"Is another process running?\n", pathname);
+		return -1;
+	}
+
+	/* we hold an exclusive lock - now downgrade it to a read lock to allow
+	 * other processes to also hold onto this file while preventing other
+	 * primaries from spinning up.
+	 */
+	retval = fcntl(mem_cfg_fd, F_SETLK, &rd_lock);
+	if (retval < 0) {
+		close(mem_cfg_fd);
+		mem_cfg_fd = -1;
+		RTE_LOG(ERR, EAL, "Cannot downgrade to shared lock on '%s': %s\n",
+			pathname, strerror(errno));
 		return -1;
 	}
 
@@ -389,6 +409,16 @@ rte_eal_config_attach(void)
 			return -1;
 		}
 	}
+	/* lock the file to prevent primary from initializing while this
+	 * process is still running.
+	 */
+	if (fcntl(mem_cfg_fd, F_SETLK, &rd_lock) < 0) {
+		close(mem_cfg_fd);
+		mem_cfg_fd = -1;
+		RTE_LOG(ERR, EAL, "Cannot create shared lock on '%s': %s\n",
+				pathname, strerror(errno));
+		return -1;
+	}
 
 	/* map it as read-only first */
 	mem_config = (struct rte_mem_config *) mmap(NULL, sizeof(*mem_config),
@@ -427,9 +457,6 @@ rte_eal_config_reattach(void)
 			sizeof(*mem_config), PROT_READ | PROT_WRITE, MAP_SHARED,
 			mem_cfg_fd, 0);
 
-	close(mem_cfg_fd);
-	mem_cfg_fd = -1;
-
 	if (mem_config == MAP_FAILED || mem_config != rte_mem_cfg_addr) {
 		if (mem_config != MAP_FAILED) {
 			/* errno is stale, don't use */
-- 
2.17.1