Hi Jia,
Could you check if the patch below resolves the bug you have reported?
Just this patch, i.e. without your proposal.
I want to leave the optimization for the get_seconds() call:
We must update sem_otime in two places anyway
(either perform_atomic_semop() and exit_sem() or
do_smart_update() and semtimedop())
--
Manfred
In commit 0a2b9d4c,the update of semaphore's sem_otime(last semop time)
was moved to one central position (do_smart_update).
But: Since do_smart_update() is only called for operations that modify
the array, this means that wait-for-zero semops do not update sem_otime
anymore.
The fix is simple:
Non-alter operations must update sem_otime.
Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
Reported-by: Jia He <jiaker...@gmail.com>
---
ipc/sem.c | 41 +++++++++++++++++++++++++++++------------
1 file changed, 29 insertions(+), 12 deletions(-)
diff --git a/ipc/sem.c b/ipc/sem.c
index e5d9bb8..ec83f79 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -910,6 +910,24 @@ again:
}
/**
+ * set_semotime(sma, sops) - set sem_otime
+ * @sma: semaphore array
+ * @sops: operations that modified the array, may be NULL
+ *
+ * sem_otime is replicated to avoid cache line trashing.
+ * This function sets one instance to the current time.
+ */
+static void set_semotime(struct sem_array *sma, struct sembuf *sops)
+{
+ if (sops == NULL) {
+ sma->sem_base[0].sem_otime = get_seconds();
+ } else {
+ sma->sem_base[sops[0].sem_num].sem_otime =
+ get_seconds();
+ }
+}
+
+/**
* do_smart_update(sma, sops, nsops, otime, pt) - optimized update_queue
* @sma: semaphore array
* @sops: operations that were performed
@@ -959,17 +977,10 @@ static void do_smart_update(struct sem_array *sma, struct
sembuf *sops, int nsop
}
}
}
- if (otime) {
- if (sops == NULL) {
- sma->sem_base[0].sem_otime = get_seconds();
- } else {
- sma->sem_base[sops[0].sem_num].sem_otime =
- get_seconds();
- }
- }
+ if (otime)
+ set_semotime(sma, sops);
}
-
/* The following counts are associated to each semaphore:
* semncnt number of tasks waiting on semval being nonzero
* semzcnt number of tasks waiting on semval being zero
@@ -1831,10 +1842,16 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf
__user *, tsops,
error = perform_atomic_semop(sma, sops, nsops, un,
task_tgid_vnr(current));
- if (error <= 0) {
- if (alter && error == 0)
+ if (error == 0) {
+ /* If the operation was successful, then do
+ * the required updates.
+ */
+ if (alter)
do_smart_update(sma, sops, nsops, 1, &tasks);
-
+ else
+ set_semotime(sma, sops);
+ }
+ if (error <= 0) {
goto out_unlock_free;
}
--
1.8.3.1
--
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