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Date: Wed, 20 Mar 2013 15:55:36 -0400
From: Rik van Riel <riel@...riel.com>
To: torvalds@...ux-foundation.org
Cc: davidlohr.bueso@...com, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, hhuang@...hat.com, jason.low2@...com,
walken@...gle.com, lwoodman@...hat.com, chegu_vinod@...com,
Rik van Riel <riel@...riel.com>,
Rik van Riel <riel@...hat.com>
Subject: [PATCH 6/7] 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@...hat.com>
---
ipc/sem.c | 65 +++++++++++++++++++++++++++++++-----------------------------
1 files changed, 34 insertions(+), 31 deletions(-)
diff --git a/ipc/sem.c b/ipc/sem.c
index d25f9b6..468e2c1 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -99,7 +99,6 @@ struct sem {
/* 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 */
@@ -517,7 +516,7 @@ static void wake_up_sem_queue_prepare(struct list_head *pt,
q->status = IN_WAKEUP;
q->pid = error;
- list_add_tail(&q->simple_list, pt);
+ list_add_tail(&q->list, pt);
}
/**
@@ -535,7 +534,7 @@ static void wake_up_sem_queue_do(struct list_head *pt)
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();
@@ -548,9 +547,7 @@ static void wake_up_sem_queue_do(struct list_head *pt)
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--;
}
@@ -603,9 +600,9 @@ static int check_restart(struct sem_array *sma, struct sem_queue *q)
}
/*
* 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);
@@ -625,8 +622,9 @@ static int check_restart(struct sem_array *sma, struct sem_queue *q)
* @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.
@@ -636,30 +634,19 @@ static int update_queue(struct sem_array *sma, int semnum, struct list_head *pt)
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
@@ -718,9 +705,18 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop
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 &&
@@ -791,6 +787,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
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);
@@ -809,6 +806,13 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
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);
@@ -1532,21 +1536,20 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
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++;
}
--
1.7.7.6
--
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