ipc,sem: have only one list in struct sem_queue
Having only one list in struct sem_queue, and only queueing simple
semaphore operations on the list for the semaphore involved, allows us to
introduce finer grained locking for semtimedop.
Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Chegu Vinod <chegu_vinod@hp.com>
Cc: Emmanuel Benisty <benisty.e@gmail.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/sem.c b/ipc/sem.c
index 7002006..f68b617 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -99,7 +99,6 @@
/* One queue for each sleeping process in the system. */
struct sem_queue {
- struct list_head simple_list; /* queue of pending operations */
struct list_head list; /* queue of pending operations */
struct task_struct *sleeper; /* this process */
struct sem_undo *undo; /* undo structure */
@@ -519,7 +518,7 @@
q->status = IN_WAKEUP;
q->pid = error;
- list_add_tail(&q->simple_list, pt);
+ list_add_tail(&q->list, pt);
}
/**
@@ -537,7 +536,7 @@
int did_something;
did_something = !list_empty(pt);
- list_for_each_entry_safe(q, t, pt, simple_list) {
+ list_for_each_entry_safe(q, t, pt, list) {
wake_up_process(q->sleeper);
/* q can disappear immediately after writing q->status. */
smp_wmb();
@@ -550,9 +549,7 @@
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
{
list_del(&q->list);
- if (q->nsops == 1)
- list_del(&q->simple_list);
- else
+ if (q->nsops > 1)
sma->complex_count--;
}
@@ -605,9 +602,9 @@
}
/*
* semval is 0. Check if there are wait-for-zero semops.
- * They must be the first entries in the per-semaphore simple queue
+ * They must be the first entries in the per-semaphore queue
*/
- h = list_first_entry(&curr->sem_pending, struct sem_queue, simple_list);
+ h = list_first_entry(&curr->sem_pending, struct sem_queue, list);
BUG_ON(h->nsops != 1);
BUG_ON(h->sops[0].sem_num != q->sops[0].sem_num);
@@ -627,8 +624,9 @@
* @pt: list head for the tasks that must be woken up.
*
* update_queue must be called after a semaphore in a semaphore array
- * was modified. If multiple semaphore were modified, then @semnum
- * must be set to -1.
+ * was modified. If multiple semaphores were modified, update_queue must
+ * be called with semnum = -1, as well as with the number of each modified
+ * semaphore.
* The tasks that must be woken up are added to @pt. The return code
* is stored in q->pid.
* The function return 1 if at least one semop was completed successfully.
@@ -638,30 +636,19 @@
struct sem_queue *q;
struct list_head *walk;
struct list_head *pending_list;
- int offset;
int semop_completed = 0;
- /* if there are complex operations around, then knowing the semaphore
- * that was modified doesn't help us. Assume that multiple semaphores
- * were modified.
- */
- if (sma->complex_count)
- semnum = -1;
-
- if (semnum == -1) {
+ if (semnum == -1)
pending_list = &sma->sem_pending;
- offset = offsetof(struct sem_queue, list);
- } else {
+ else
pending_list = &sma->sem_base[semnum].sem_pending;
- offset = offsetof(struct sem_queue, simple_list);
- }
again:
walk = pending_list->next;
while (walk != pending_list) {
int error, restart;
- q = (struct sem_queue *)((char *)walk - offset);
+ q = container_of(walk, struct sem_queue, list);
walk = walk->next;
/* If we are scanning the single sop, per-semaphore list of
@@ -720,9 +707,18 @@
if (sma->complex_count || sops == NULL) {
if (update_queue(sma, -1, pt))
otime = 1;
+ }
+
+ if (!sops) {
+ /* No semops; something special is going on. */
+ for (i = 0; i < sma->sem_nsems; i++) {
+ if (update_queue(sma, i, pt))
+ otime = 1;
+ }
goto done;
}
+ /* Check the semaphores that were modified. */
for (i = 0; i < nsops; i++) {
if (sops[i].sem_op > 0 ||
(sops[i].sem_op < 0 &&
@@ -793,6 +789,7 @@
struct sem_queue *q, *tq;
struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
struct list_head tasks;
+ int i;
/* Free the existing undo structures for this semaphore set. */
assert_spin_locked(&sma->sem_perm.lock);
@@ -811,6 +808,13 @@
unlink_queue(sma, q);
wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
}
+ for (i = 0; i < sma->sem_nsems; i++) {
+ struct sem *sem = sma->sem_base + i;
+ list_for_each_entry_safe(q, tq, &sem->sem_pending, list) {
+ unlink_queue(sma, q);
+ wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
+ }
+ }
/* Remove the semaphore set from the IDR */
sem_rmid(ns, sma);
@@ -1565,21 +1569,20 @@
queue.undo = un;
queue.pid = task_tgid_vnr(current);
queue.alter = alter;
- if (alter)
- list_add_tail(&queue.list, &sma->sem_pending);
- else
- list_add(&queue.list, &sma->sem_pending);
if (nsops == 1) {
struct sem *curr;
curr = &sma->sem_base[sops->sem_num];
if (alter)
- list_add_tail(&queue.simple_list, &curr->sem_pending);
+ list_add_tail(&queue.list, &curr->sem_pending);
else
- list_add(&queue.simple_list, &curr->sem_pending);
+ list_add(&queue.list, &curr->sem_pending);
} else {
- INIT_LIST_HEAD(&queue.simple_list);
+ if (alter)
+ list_add_tail(&queue.list, &sma->sem_pending);
+ else
+ list_add(&queue.list, &sma->sem_pending);
sma->complex_count++;
}