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Date: Sun, 18 Apr 2010 19:07:16 +0200
From: Manfred Spraul <manfred@...orfullife.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Chris Mason <chris.mason@...cle.com>,
Zach Brown <zach.brown@...cle.com>,
Jens Axboe <jens.axboe@...cle.com>,
Nick Piggin <npiggin@...e.de>,
Manfred Spraul <manfred@...orfullife.com>
Subject: [PATCH 2/3] [PATCH] ipc/sem.c: move wake_up_process out of the spinlock section
For the sysv sem code, waking up a tasks consists out of two steps:
- the right tasks must be identified.
- they must be woken up.
Right now, both steps run while the array spinlock is held.
This patch reorders the code and moves the actual wake_up_process()
behind the point where the spinlock is dropped.
---
ipc/sem.c | 111 +++++++++++++++++++++++++++++++++++++++++++-----------------
1 files changed, 79 insertions(+), 32 deletions(-)
diff --git a/ipc/sem.c b/ipc/sem.c
index efadb6d..34ae151 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -381,7 +381,6 @@ static int try_atomic_semop (struct sem_array * sma, struct sembuf * sops,
sop--;
}
- sma->sem_otime = get_seconds();
return 0;
out_of_range:
@@ -404,25 +403,41 @@ undo:
return result;
}
-/*
- * Wake up a process waiting on the sem queue with a given error.
- * The queue is invalid (may not be accessed) after the function returns.
+/** wake_up_sem_queue_prepare(q, error): Prepare wake-up
+ * @q: queue entry that must be signaled
+ * @error: Error value for the signal
+ *
+ * Prepare the wake-up of the queue entry q.
*/
-static void wake_up_sem_queue(struct sem_queue *q, int error)
+static void wake_up_sem_queue_prepare(struct list_head *pt, struct sem_queue *q, int error)
{
- /*
- * Hold preempt off so that we don't get preempted and have the
- * wakee busy-wait until we're scheduled back on. We're holding
- * locks here so it may not strictly be needed, however if the
- * locks become preemptible then this prevents such a problem.
- */
- preempt_disable();
+ if (list_empty(pt)) {
+ /*
+ * Hold preempt off so that we don't get preempted and have the
+ * wakee busy-wait until we're scheduled back on.
+ */
+ preempt_disable();
+ }
q->status = IN_WAKEUP;
- wake_up_process(q->sleeper);
- /* hands-off: q can disappear immediately after writing q->status. */
- smp_wmb();
- q->status = error;
- preempt_enable();
+ q->pid = error;
+
+ list_add_tail(&q->simple_list, pt);
+}
+
+static void wake_up_sem_queue_do(struct list_head *pt)
+{
+ struct sem_queue *q, *t;
+ int did_something;
+
+ did_something = !list_empty(pt);
+ list_for_each_entry_safe(q, t, pt, simple_list) {
+ wake_up_process(q->sleeper);
+ /* hands-off: q can disappear immediately after writing q->status. */
+ smp_wmb();
+ q->status = q->pid;
+ }
+ if (did_something)
+ preempt_enable();
}
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
@@ -502,17 +517,22 @@ static int check_restart(struct sem_array *sma, struct sem_queue *q)
* update_queue(sma, semnum): Look for tasks that can be completed.
* @sma: semaphore array.
* @semnum: semaphore that was modified.
+ * @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.
+ * 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 array variable was modified.
*/
-static void update_queue(struct sem_array *sma, int semnum)
+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 retval;
/* if there are complex operations around, then knowing the semaphore
* that was modified doesn't help us. Assume that multiple semaphores
@@ -556,40 +576,54 @@ again:
continue;
unlink_queue(sma, q);
+ if (q->alter)
+ retval = 1;
if (error)
restart = 0;
else
restart = check_restart(sma, q);
- wake_up_sem_queue(q, error);
+ wake_up_sem_queue_prepare(pt, q, error);
if (restart)
goto again;
}
+ return retval;
}
-/** do_smart_update(sma, sops, nsops): Optimized update_queue
+/** do_smart_update(sma, sops, nsops, otime, pt): Optimized update_queue
* @sma: semaphore array
* @sops: operations that were performed
* @nsops: number of operations
+ * @otime: force setting otime
+ * @pt: list head of the tasks that must be woken up.
*
* do_smart_update() does the required called to update_queue, based on the
* actual changes that were performed on the semaphore array.
+ * Note that the function does not do the actual wake-up: the caller is
+ * responsible for calling wake_up_sem_queue_do(@pt).
+ * It is safe to perform this call after dropping all locks.
*/
-void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops)
+void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
+ int otime, struct list_head *pt)
{
int i;
if (sma->complex_count) {
- update_queue(sma, -1);
- return;
+ if (update_queue(sma, -1, pt))
+ otime = 1;
+ goto done;
}
for (i=0;i<nsops;i++) {
if (sops[i].sem_op > 0 ||
(sops[i].sem_op < 0 && sma->sem_base[sops[i].sem_num].semval == 0))
- update_queue(sma, sops[i].sem_num);
+ if (update_queue(sma, sops[i].sem_num, pt))
+ otime = 1;
}
+done:
+ if (otime)
+ sma->sem_otime = get_seconds();
}
@@ -655,6 +689,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
struct sem_undo *un, *tu;
struct sem_queue *q, *tq;
struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
+ struct list_head tasks;
/* Free the existing undo structures for this semaphore set. */
assert_spin_locked(&sma->sem_perm.lock);
@@ -668,15 +703,17 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
}
/* Wake up all pending processes and let them fail with EIDRM. */
+ INIT_LIST_HEAD(&tasks);
list_for_each_entry_safe(q, tq, &sma->sem_pending, list) {
unlink_queue(sma, q);
- wake_up_sem_queue(q, -EIDRM);
+ wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
}
/* Remove the semaphore set from the IDR */
sem_rmid(ns, sma);
sem_unlock(sma);
+ wake_up_sem_queue_do(&tasks);
ns->used_sems -= sma->sem_nsems;
security_sem_free(sma);
ipc_rcu_putref(sma);
@@ -798,11 +835,13 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
ushort fast_sem_io[SEMMSL_FAST];
ushort* sem_io = fast_sem_io;
int nsems;
+ struct list_head tasks;
sma = sem_lock_check(ns, semid);
if (IS_ERR(sma))
return PTR_ERR(sma);
+ INIT_LIST_HEAD(&tasks);
nsems = sma->sem_nsems;
err = -EACCES;
@@ -890,7 +929,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma, -1);
+ do_smart_update(sma, NULL, 0, 0, &tasks);
err = 0;
goto out_unlock;
}
@@ -932,13 +971,15 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
curr->sempid = task_tgid_vnr(current);
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma, semnum);
+ do_smart_update(sma, NULL, 0, 0, &tasks);
err = 0;
goto out_unlock;
}
}
out_unlock:
sem_unlock(sma);
+ wake_up_sem_queue_do(&tasks);
+
out_free:
if(sem_io != fast_sem_io)
ipc_free(sem_io, sizeof(ushort)*nsems);
@@ -1212,6 +1253,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
struct sem_queue queue;
unsigned long jiffies_left = 0;
struct ipc_namespace *ns;
+ struct list_head tasks;
ns = current->nsproxy->ipc_ns;
@@ -1260,6 +1302,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
} else
un = NULL;
+ INIT_LIST_HEAD(&tasks);
+
sma = sem_lock_check(ns, semid);
if (IS_ERR(sma)) {
if (un)
@@ -1307,9 +1351,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
error = try_atomic_semop (sma, sops, nsops, un, task_tgid_vnr(current));
if (error <= 0) {
- if (alter && error == 0) {
- do_smart_update(sma, sops, nsops);
- }
+ if (alter && error == 0)
+ do_smart_update(sma, sops, nsops, 1, &tasks);
goto out_unlock_free;
}
@@ -1386,6 +1429,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
out_unlock_free:
sem_unlock(sma);
+
+ wake_up_sem_queue_do(&tasks);
out_free:
if(sops != fast_sops)
kfree(sops);
@@ -1446,6 +1491,7 @@ void exit_sem(struct task_struct *tsk)
for (;;) {
struct sem_array *sma;
struct sem_undo *un;
+ struct list_head tasks;
int semid;
int i;
@@ -1509,10 +1555,11 @@ void exit_sem(struct task_struct *tsk)
semaphore->sempid = task_tgid_vnr(current);
}
}
- sma->sem_otime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma, -1);
+ INIT_LIST_HEAD(&tasks);
+ do_smart_update(sma, NULL, 0, 1, &tasks);
sem_unlock(sma);
+ wake_up_sem_queue_do(&tasks);
call_rcu(&un->rcu, free_un);
}
--
1.6.6.1
--
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