linux-kernel - [PATCH 3.4 01/65] hrtimer: Allow concurrent hrtimer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1445302095-4695-1-git-send-email-lizf@kernel.org>
Date:	Tue, 20 Oct 2015 08:47:11 +0800
From:	lizf@...nel.org
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ben Segall <bsegall@...gle.com>,
	Roman Gushchin <klamm@...dex-team.ru>,
	Paul Turner <pjt@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 01/65] hrtimer: Allow concurrent hrtimer_start() for self restarting timers

From: Peter Zijlstra <peterz@...radead.org>

3.4.110-rc1 review patch.  If anyone has any objections, please let me know.

------------------


commit 5de2755c8c8b3a6b8414870e2c284914a2b42e4d upstream.

Because we drop cpu_base->lock around calling hrtimer::function, it is
possible for hrtimer_start() to come in between and enqueue the timer.

If hrtimer::function then returns HRTIMER_RESTART we'll hit the BUG_ON
because HRTIMER_STATE_ENQUEUED will be set.

Since the above is a perfectly valid scenario, remove the BUG_ON and
make the enqueue_hrtimer() call conditional on the timer not being
enqueued already.

NOTE: in that concurrent scenario its entirely common for both sites
to want to modify the hrtimer, since hrtimers don't provide
serialization themselves be sure to provide some such that the
hrtimer::function and the hrtimer_start() caller don't both try and
fudge the expiration state at the same time.

To that effect, add a WARN when someone tries to forward an already
enqueued timer, the most common way to change the expiry of self
restarting timers. Ideally we'd put the WARN in everything modifying
the expiry but most of that is inlines and we don't need the bloat.

Fixes: 2d44ae4d7135 ("hrtimer: clean up cpu->base locking tricks")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Roman Gushchin <klamm@...dex-team.ru>
Cc: Paul Turner <pjt@...gle.com>
Link: http://lkml.kernel.org/r/20150415113105.GT5029@twins.programming.kicks-ass.net
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Zefan Li <lizefan@...wei.com>
---
 kernel/hrtimer.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 434f2b6..34031a0 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -853,6 +853,9 @@ u64 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval)
 	if (delta.tv64 < 0)
 		return 0;
 
+	if (WARN_ON(timer->state & HRTIMER_STATE_ENQUEUED))
+		return 0;
+
 	if (interval.tv64 < timer->base->resolution.tv64)
 		interval.tv64 = timer->base->resolution.tv64;
 
@@ -1265,11 +1268,14 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
 	 * Note: We clear the CALLBACK bit after enqueue_hrtimer and
 	 * we do not reprogramm the event hardware. Happens either in
 	 * hrtimer_start_range_ns() or in hrtimer_interrupt()
+	 *
+	 * Note: Because we dropped the cpu_base->lock above,
+	 * hrtimer_start_range_ns() can have popped in and enqueued the timer
+	 * for us already.
 	 */
-	if (restart != HRTIMER_NORESTART) {
-		BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
+	if (restart != HRTIMER_NORESTART &&
+	    !(timer->state & HRTIMER_STATE_ENQUEUED))
 		enqueue_hrtimer(timer, base);
-	}
 
 	WARN_ON_ONCE(!(timer->state & HRTIMER_STATE_CALLBACK));
 
-- 
1.9.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/