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From: Anna-Maria Gleixner <anna-maria@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	keescook@chromium.org, Christoph Hellwig <hch@lst.de>,
	John Stultz <john.stultz@linaro.org>,
	Anna-Maria Gleixner <anna-maria@linutronix.de>
Subject: [PATCH v3 02/36] hrtimer: Correct blantanly wrong comment
Date: Wed, 29 Nov 2017 16:30:27 +0100	[thread overview]
Message-ID: <20171129153101.27297-3-anna-maria@linutronix.de> (raw)
In-Reply-To: <20171129153101.27297-1-anna-maria@linutronix.de>

From: Thomas Gleixner <tglx@linutronix.de>

The protection of a hrtimer which runs its callback against migration to a
different CPU has nothing to do with hard interrupt context.

The protection against migration of a hrtimer running the expiry callback
is the pointer in the cpu_base which holds a pointer to the currently
running timer. This pointer is evaluated in the code which potentially
switches the timer base and makes sure it's kept on the CPU on which the
callback is running.

Reported-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
---
 kernel/time/hrtimer.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 69d203d8b12d..aee49c0c58b9 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1195,9 +1195,9 @@ static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
 		timer->is_rel = false;
 
 	/*
-	 * Because we run timers from hardirq context, there is no chance
-	 * they get migrated to another cpu, therefore its safe to unlock
-	 * the timer base.
+	 * The timer is marked as running in the cpu base, so it is
+	 * protected against migration to a different CPU even if the lock
+	 * is dropped.
 	 */
 	raw_spin_unlock(&cpu_base->lock);
 	trace_hrtimer_expire_entry(timer, now);
-- 
2.11.0

  parent reply	other threads:[~2017-11-29 15:45 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-29 15:30 [PATCH 00/36] hrtimer: Provide softirq context hrtimers Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 01/36] timers: Use static keys for migrate_enable/nohz_active Anna-Maria Gleixner
2017-11-29 15:30 ` Anna-Maria Gleixner [this message]
2017-11-29 15:30 ` [PATCH v3 03/36] hrtimer: Fix kerneldoc for struct hrtimer_cpu_base Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 04/36] hrtimer: Cleanup clock argument in schedule_hrtimeout_range_clock() Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 05/36] hrtimer: Fix hrtimer function description Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 06/36] hrtimer: Ensure POSIX compliance (relative CLOCK_REALTIME hrtimers) Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 07/36] hrtimer: Cleanup hrtimer_mode enum Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 08/36] tracing/hrtimer: Take all clock bases and modes into account Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 09/36] tracing/hrtimer: Print hrtimer mode in hrtimer_start tracepoint Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 10/36] hrtimer: Switch for loop to _ffs() evaluation Anna-Maria Gleixner
2017-11-29 16:06   ` Joe Perches
2017-11-29 15:30 ` [PATCH v3 11/36] hrtimer: Store running timer in hrtimer_clock_base Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 12/36] hrtimer: Make room in struct hrtimer_cpu_base Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 13/36] hrtimer: Reduce conditional code (hres_active) Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 14/36] hrtimer: Use accesor functions instead of direct access Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 15/36] hrtimer: Make the remote enqueue check unconditional Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 16/36] hrtimer: Make hrtimer_cpu_base.next_timer handling unconditional Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 17/36] hrtimer: Make hrtimer_reprogramm() unconditional Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 18/36] hrtimer: Make hrtimer_force_reprogramm() unconditionally available Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 19/36] hrtimer: Unify handling of hrtimer remove Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 20/36] hrtimer: Unify handling of remote enqueue Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 21/36] hrtimer: Make remote enqueue decision less restrictive Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 22/36] hrtimer: Remove base argument from hrtimer_reprogram() Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 23/36] hrtimer: Split hrtimer_start_range_ns() Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 24/36] hrtimer: Split __hrtimer_get_next_event() Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 25/36] hrtimer: Use irqsave/irqrestore around __run_hrtimer() Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 26/36] hrtimer: Add clock bases and hrtimer mode for soft irq context Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 27/36] hrtimer: Prepare handling of hard and softirq based hrtimers Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 28/36] hrtimer: Implement support for " Anna-Maria Gleixner
2017-12-14 10:47   ` Sebastian Andrzej Siewior
2017-11-29 15:30 ` [PATCH v3 29/36] hrtimer: Implement SOFT/HARD clock base selection Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 30/36] can/bcm: Replace hrtimer_tasklet with softirq based hrtimer Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 31/36] mac80211_hwsim: Replace hrtimer tasklet with softirq hrtimer Anna-Maria Gleixner
2017-12-11 11:27   ` Johannes Berg
2017-11-29 15:30 ` [PATCH v3 32/36] xfrm: " Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 33/36] softirq: Remove tasklet_hrtimer Anna-Maria Gleixner
2017-11-29 15:30 ` [PATCH v3 34/36] ALSA/dummy: Replace tasklet with softirq hrtimer Anna-Maria Gleixner
2017-11-29 15:30   ` Anna-Maria Gleixner
2017-12-06 16:27   ` Takashi Iwai
2017-12-06 16:27     ` Takashi Iwai
2017-11-29 15:31 ` [PATCH v3 35/36] usb/gadget/NCM: " Anna-Maria Gleixner
2017-12-04 13:14   ` Felipe Balbi
2017-12-07  7:35     ` Anna-Maria Gleixner
2017-11-29 15:31 ` [PATCH v3 36/36] net/mvpp2: " Anna-Maria Gleixner

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