76 lines
2.1 KiB
Diff
76 lines
2.1 KiB
Diff
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From 68026d4505c17ce86ee21feb4096b3318ad95db0 Mon Sep 17 00:00:00 2001
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From: Peter Zijlstra <peterz@infradead.org>
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Date: Wed, 14 Sep 2011 11:57:04 +0200
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Subject: [PATCH 265/365] ipc/sem: Rework semaphore wakeups
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Current sysv sems have a weird ass wakeup scheme that involves keeping
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preemption disabled over a potential O(n^2) loop and busy waiting on
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that on other CPUs.
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Kill this and simply wake the task directly from under the sem_lock.
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This was discovered by a migrate_disable() debug feature that
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disallows:
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spin_lock();
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preempt_disable();
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spin_unlock()
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preempt_enable();
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Cc: Manfred Spraul <manfred@colorfullife.com>
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Suggested-by: Thomas Gleixner <tglx@linutronix.de>
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Reported-by: Mike Galbraith <efault@gmx.de>
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Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
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Cc: Manfred Spraul <manfred@colorfullife.com>
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Link: http://lkml.kernel.org/r/1315994224.5040.1.camel@twins
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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ipc/sem.c | 10 ++++++++++
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1 file changed, 10 insertions(+)
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diff --git a/ipc/sem.c b/ipc/sem.c
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index 5cd9d802592f..c987efce266f 100644
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--- a/ipc/sem.c
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+++ b/ipc/sem.c
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@@ -712,6 +712,13 @@ static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
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static void wake_up_sem_queue_prepare(struct list_head *pt,
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struct sem_queue *q, int error)
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{
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+#ifdef CONFIG_PREEMPT_RT_BASE
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+ struct task_struct *p = q->sleeper;
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+ get_task_struct(p);
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+ q->status = error;
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+ wake_up_process(p);
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+ put_task_struct(p);
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+#else
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if (list_empty(pt)) {
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/*
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* Hold preempt off so that we don't get preempted and have the
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@@ -723,6 +730,7 @@ static void wake_up_sem_queue_prepare(struct list_head *pt,
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q->pid = error;
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list_add_tail(&q->list, pt);
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+#endif
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}
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/**
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@@ -736,6 +744,7 @@ static void wake_up_sem_queue_prepare(struct list_head *pt,
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*/
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static void wake_up_sem_queue_do(struct list_head *pt)
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{
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+#ifndef CONFIG_PREEMPT_RT_BASE
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struct sem_queue *q, *t;
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int did_something;
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@@ -748,6 +757,7 @@ static void wake_up_sem_queue_do(struct list_head *pt)
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}
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if (did_something)
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preempt_enable();
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+#endif
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}
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static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
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--
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2.28.0
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