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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>
This commit is contained in:
Rik van Riel 2013-04-30 19:15:39 -07:00 committed by Linus Torvalds
parent c460b662d5
commit 9f1bc2c902
1 changed files with 34 additions and 31 deletions
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65
ipc/sem.c
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@ -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 */
@ -519,7 +518,7 @@ 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);
}
/**
@ -537,7 +536,7 @@ 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();
@ -550,9 +549,7 @@ 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--;
}
@ -605,9 +602,9 @@ 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);
@ -627,8 +624,9 @@ 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.
@ -638,30 +636,19 @@ 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
@ -720,9 +707,18 @@ 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 &&
@ -793,6 +789,7 @@ 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);
@ -811,6 +808,13 @@ 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);
@ -1565,21 +1569,20 @@ 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++;
}