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Commit 9f1bc2c9 authored by Rik van Riel's avatar Rik van Riel Committed by Linus Torvalds
Browse files

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: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarDavidlohr 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: default avatarSedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c460b662

ipc/sem.c

+34 −31
Original line number Diff line number Diff line
@@ -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++;

	}