linux-kernel - [tip:timers/core] hrtimer: Make remote enqueue decision less restrictive

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Message-ID: <tip-2ac2dccce9d16a7b1a8fddf69a955d249375bce4@git.kernel.org>
Date:   Mon, 15 Jan 2018 19:49:07 -0800
From:   tip-bot for Anna-Maria Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, hch@....de, tglx@...utronix.de,
        mingo@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com,
        peterz@...radead.org, john.stultz@...aro.org,
        anna-maria@...utronix.de
Subject: [tip:timers/core] hrtimer: Make remote enqueue decision less
 restrictive

Commit-ID:  2ac2dccce9d16a7b1a8fddf69a955d249375bce4
Gitweb:     https://git.kernel.org/tip/2ac2dccce9d16a7b1a8fddf69a955d249375bce4
Author:     Anna-Maria Gleixner <anna-maria@...utronix.de>
AuthorDate: Thu, 21 Dec 2017 11:41:50 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 16 Jan 2018 02:53:58 +0100

hrtimer: Make remote enqueue decision less restrictive

The current decision whether a timer can be queued on a remote CPU checks
for timer->expiry <= remote_cpu_base.expires_next.

This is too restrictive because a timer with the same expiry time as an
existing timer will be enqueued on right-hand size of the existing timer
inside the rbtree, i.e. behind the first expiring timer.

So its safe to allow enqueuing timers with the same expiry time as the
first expiring timer on a remote CPU base.

Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc: Christoph Hellwig <hch@....de>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: keescook@...omium.org
Link: http://lkml.kernel.org/r/20171221104205.7269-22-anna-maria@linutronix.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/time/hrtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 1c68bf2..f4a56fb 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -168,7 +168,7 @@ hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)
 	ktime_t expires;
 
 	expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset);
-	return expires <= new_base->cpu_base->expires_next;
+	return expires < new_base->cpu_base->expires_next;
 }
 
 static inline