Currently IPC_RMID was attempted on a semid returned after failed
semget() with flags=IPC_CREAT|IPC_EXCL. So nothing was actually removed.
To get a proper semid, this patch retries semget() without IPC_EXCL.
This opens up a race: if the lock-tester grabbed the old sem before
lock-setter used that magic to remove it, then the lock-tester will
remain with removed sem.
Additionally locker was waiting for sem_otime on sem0 to became
non-zero after incrementing sem0 himself. So sem_otime was never
0 at the time of checking it.
So basically the code was all wrong.
This patch:
- fixes RMID after IPC_EXCL to actually remove the sem
- moves the increment of sem1 to the lock-tester site, and the
lock-setter waits for that event
- replaces the wait loop on sem_otime with GETVAL, adding a small sleep.
- lock-tester during the init sequence checks for removed sem, and
if it is - retries the init from semget()
Signed-off-by: Stas Sergeev <stsp2@xxxxxxxxx>
---
src/t_ofd_locks.c | 73 ++++++++++++++++++++++++++++++-----------------
1 file changed, 47 insertions(+), 26 deletions(-)
diff --git a/src/t_ofd_locks.c b/src/t_ofd_locks.c
index e77f2659..daa6f96c 100644
--- a/src/t_ofd_locks.c
+++ b/src/t_ofd_locks.c
@@ -297,6 +297,7 @@ int main(int argc, char **argv)
semid = semget(semkey, 2, IPC_CREAT|IPC_EXCL);
if (semid < 0 && errno == EEXIST) {
/* remove sem set after one round of test */
+ semid = semget(semkey, 2, IPC_CREAT);
if (semctl(semid, 2, IPC_RMID, semu) == -1)
err_exit("rmid 0", errno);
retry++;
@@ -315,32 +316,29 @@ int main(int argc, char **argv)
semu.array = vals;
if (semctl(semid, 2, SETALL, semu) == -1)
err_exit("init sem", errno);
- /* Inc both new sem to 2 */
- sop.sem_num = 0;
- sop.sem_op = 1;
- sop.sem_flg = 0;
- ts.tv_sec = 5;
- ts.tv_nsec = 0;
- if (semtimedop(semid, &sop, 1, &ts) == -1)
- err_exit("inc sem0 2", errno);
- sop.sem_num = 1;
- sop.sem_op = 1;
- sop.sem_flg = 0;
- ts.tv_sec = 5;
- ts.tv_nsec = 0;
- if (semtimedop(semid, &sop, 1, &ts) == -1)
- err_exit("inc sem1 2", errno);
/*
- * Wait initialization complete. semctl(2) only update
- * sem_ctime, semop(2) will update sem_otime.
+ * Wait initialization complete.
*/
ret = -1;
do {
+ if (ret != -1)
+ usleep(100000);
memset(&sem_ds, 0, sizeof(sem_ds));
semu.buf = &sem_ds;
- ret = semctl(semid, 0, IPC_STAT, semu);
- } while (!(ret == 0 && sem_ds.sem_otime != 0));
+ ret = semctl(semid, 1, GETVAL, semu);
+ if (ret == -1)
+ err_exit("wait sem1 2", errno);
+ } while (ret != 2);
+
+ /* Inc sem0 to 2 */
+ sop.sem_num = 0;
+ sop.sem_op = 1;
+ sop.sem_flg = 0;
+ ts.tv_sec = 5;
+ ts.tv_nsec = 0;
+ if (semtimedop(semid, &sop, 1, &ts) == -1)
+ err_exit("inc sem0 2", errno);
/* place the lock */
if (fcntl(fd, setlk_macro, &flk) < 0)
@@ -393,10 +391,26 @@ int main(int argc, char **argv)
/* getlck */
if (lock_cmd == 0) {
/* wait sem created and initialized */
+again:
retry = 5;
do {
semid = semget(semkey, 2, 0);
- if (semid != -1)
+ ret = -1;
+ if (semid != -1) do {
+ if (ret != -1)
+ usleep(100000);
+ memset(&sem_ds, 0, sizeof(sem_ds));
+ semu.buf = &sem_ds;
+ ret = semctl(semid, 0, GETVAL, semu);
+ if (ret == -1 && (errno == EINVAL
+ || errno == EIDRM)) {
+ /* sem removed */
+ goto again;
+ }
+ if (ret == -1)
+ break;
+ } while (ret != 1);
+ if (ret == 1)
break;
if (errno == ENOENT && retry) {
sleep(1);
@@ -406,11 +420,15 @@ int main(int argc, char **argv)
err_exit("getlk_semget", errno);
}
} while (1);
- do {
- memset(&sem_ds, 0, sizeof(sem_ds));
- semu.buf = &sem_ds;
- ret = semctl(semid, 0, IPC_STAT, semu);
- } while (!(ret == 0 && sem_ds.sem_otime != 0));
+
+ /* inc sem1 to 2 (initialization completed) */
+ sop.sem_num = 1;
+ sop.sem_op = 1;
+ sop.sem_flg = 0;
+ ts.tv_sec = 5;
+ ts.tv_nsec = 0;
+ if (semtimedop(semid, &sop, 1, &ts) == -1)
+ err_exit("inc sem1 2", errno);
/* wait sem0 == 0 (setlk and close fd done) */
sop.sem_num = 0;
@@ -418,8 +436,11 @@ int main(int argc, char **argv)
sop.sem_flg = 0;
ts.tv_sec = 5;
ts.tv_nsec = 0;
- if (semtimedop(semid, &sop, 1, &ts) == -1)
+ if (semtimedop(semid, &sop, 1, &ts) == -1) {
+ if (errno == EIDRM || errno == EINVAL)
+ goto again;
err_exit("wait sem0 0", errno);
+ }
if (fcntl(fd, getlk_macro, &flk) < 0)
err_exit("getlk", errno);
--
2.39.2
