73 lines
2.8 KiB
Diff
73 lines
2.8 KiB
Diff
From 6dc7943d18c67e3ed723cac7e4ea01f6fcd44e9d Mon Sep 17 00:00:00 2001
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Message-Id: <6dc7943d18c67e3ed723cac7e4ea01f6fcd44e9d.1599166691.git.zanussi@kernel.org>
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In-Reply-To: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
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References: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
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From: Corey Minyard <cminyard@mvista.com>
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Date: Thu, 9 May 2019 14:33:20 -0500
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Subject: [PATCH 265/333] sched/completion: Fix a lockup in
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wait_for_completion()
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.142-rt63.tar.xz
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Consider following race:
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T0 T1 T2
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wait_for_completion()
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do_wait_for_common()
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__prepare_to_swait()
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schedule()
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complete()
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x->done++ (0 -> 1)
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raw_spin_lock_irqsave()
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swake_up_locked() wait_for_completion()
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wake_up_process(T0)
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list_del_init()
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raw_spin_unlock_irqrestore()
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raw_spin_lock_irq(&x->wait.lock)
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raw_spin_lock_irq(&x->wait.lock) x->done != UINT_MAX, 1 -> 0
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raw_spin_unlock_irq(&x->wait.lock)
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return 1
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while (!x->done && timeout),
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continue loop, not enqueued
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on &x->wait
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Basically, the problem is that the original wait queues used in
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completions did not remove the item from the queue in the wakeup
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function, but swake_up_locked() does.
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Fix it by adding the thread to the wait queue inside the do loop.
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The design of swait detects if it is already in the list and doesn't
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do the list add again.
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Cc: stable-rt@vger.kernel.org
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Fixes: a04ff6b4ec4ee7e ("completion: Use simple wait queues")
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Signed-off-by: Corey Minyard <cminyard@mvista.com>
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Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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[bigeasy: shorten commit message ]
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/sched/completion.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
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index 755a58084978..49c14137988e 100644
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--- a/kernel/sched/completion.c
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+++ b/kernel/sched/completion.c
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@@ -72,12 +72,12 @@ do_wait_for_common(struct completion *x,
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if (!x->done) {
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DECLARE_SWAITQUEUE(wait);
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- __prepare_to_swait(&x->wait, &wait);
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do {
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if (signal_pending_state(state, current)) {
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timeout = -ERESTARTSYS;
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break;
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}
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+ __prepare_to_swait(&x->wait, &wait);
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__set_current_state(state);
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raw_spin_unlock_irq(&x->wait.lock);
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timeout = action(timeout);
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--
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2.17.1
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