Hi Rik,
On 05/20/2013 12:32 AM, Rik van Riel wrote:
@@ -751,17 +744,19 @@ static int update_queue(struct sem_array *sma, int
semnum, struct list_head *pt)
static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int
nsops,
int otime, struct list_head *pt)
{
- int i;
+ int i, restart;
+ again:
+ restart = 0;
if (sma->complex_count || sops == NULL) {
- if (update_queue(sma, -1, pt))
+ if (update_queue(sma, -1, pt, &restart))
otime = 1;
}
I didn't notice it immediately, this is insufficient:
Complex operations may affect all semaphores in the array.
Thus it is not sufficient to scan the per-semaphore queues of the
semaphores that were touched by *sops, all must be scanned.
Perhaps something like:
> + if (update_queue(sma, -1, pt, &restart))
> + sops = NULL;
> otime = 1;
> }
(untested!)
Test case:
1: semop(<key>, {{1, -1, 0}, {2, 1, 0}}, 2 <unfinished ...>
2: semop(<key>, {{2, -1, 0}}, 1 <unfinished ...>
3: semop(<key>, {{1, 1, 0}}, 1) = 0
[3] is able to run, calls do_smart_update().
The global queue is scanned and [1] is released
Without the "sops = NULL", [2] sleeps forever.
--
Manfred
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