src/bindings: prevent duplicate entries in the pid hash table from appear

Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>

Author: mihalicyn

src/bindings.c

@@ -566,15 +566,29 @@ pid_t lookup_initpid_in_store(pid_t pid)
 
 	hashed_pid = lookup_verify_initpid(st.st_ino);
 	if (hashed_pid < 0) {
+		pid_t already_hashed_pid;
+
 		/* release the mutex as the following call is expensive */
 		store_unlock();
 
 		hashed_pid = scm_init_pid(pid);
 
 		store_lock();
 
-		if (hashed_pid > 0)
-			save_initpid(st.st_ino, hashed_pid);
+		/* recheck that entry wasn't added while lock was released */
+		already_hashed_pid = lookup_verify_initpid(st.st_ino);
+
+		/* no existing entry found. Just add a new one. */
+		if (already_hashed_pid < 0) {
+			if (hashed_pid > 0)
+				save_initpid(st.st_ino, hashed_pid);
+
+		/* entry found it must have the same pid */
+		} else if (already_hashed_pid != hashed_pid) {
+			lxcfs_error("Different init pids (%d, %d) for the same cache entry %lu\n",
+				    already_hashed_pid, hashed_pid, HASH(st.st_ino));
+			hashed_pid = -1;
+		}
 	}
 
 	/*