Fix issue when stepping through two processes calling fr_sem_get

diff --git a/src/lib/util/sem.c b/src/lib/util/sem.c
index fba1ab6b8999cceed9d0bec59ac6e06fa1e49fd7..e34cc62a8b1258e98bc169050818adfa6a6c386e 100644 (file)
--- a/src/lib/util/sem.c
+++ b/src/lib/util/sem.c
@@ -342,8 +342,9 @@ static bool sem_check_gid(char const *file, int proj_id,
  */
 int fr_sem_get(char const *file, int proj_id, bool check_perm)
 {
-       key_t sem_key;
-       int sem_id;
+       key_t   sem_key;
+       int     sem_id;
+       bool    seen_eexist = false;
 
        if (proj_id == 0) proj_id = DEFAULT_PROJ_ID;
 
@@ -357,6 +358,7 @@ int fr_sem_get(char const *file, int proj_id, bool check_perm)
        /*
         *      Try and grab the existing semaphore
         */
+again:
        sem_id = semget(sem_key, 0, 0);
        if (sem_id < 0) {
                if (errno != ENOENT) {  /* Semaphore existed but we ran into an error */
@@ -372,6 +374,13 @@ int fr_sem_get(char const *file, int proj_id, bool check_perm)
                sem_id = semget(sem_key, 1,
                                IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH);
                if (sem_id < 0) {
+                       if (errno == EEXIST) {  /* Can get this with racing processes */
+                               if (!seen_eexist) {
+                                       seen_eexist = true;
+                                       goto again;
+                               }
+                       }
+
                        fr_strerror_printf("Failed creating semaphore on \"%s\" ID 0x%x: %s",
                                           file, proj_id, fr_syserror(errno));
                        return -3;