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 70020066ac0daaee126beee5b69ae6c278a5da13..f68b61749a85eda29a033126ae3efa98cf8916a3 100644 (file)
--- 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 */
@@ -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++;
        }