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Date: Fri, 17 Apr 2015 15:27:26 +0200
From: Ingo Tuchscherer <ingo.tuchscherer@...ibm.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, mschwid2@...ux.vnet.ibm.com,
heicars2@...ux.vnet.ibm.com, linux-s390@...r.kernel.org
Subject: Re: [patch 2/5] s390: crypto: Protect poll timeout update
You're right. Thanks for pointing this out.
I'll fix these issues and bring them upstream.
Mit freundlichen Grüßen / Kind regards
Ingo Tuchscherer
Software Development - Linux on z Systems
IBM Systems &Technology Group
Phone: +49-7031-16-1986 IBM Deutschland (Embedded
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243294
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar
<mingo@...nel.org>, Ingo Tuchscherer/Germany/IBM@...DE,
mschwid2@...ux.vnet.ibm.com, heicars2@...ux.vnet.ibm.com,
linux-s390@...r.kernel.org
Date: 04/13/2015 11:02 PM
Subject: [patch 2/5] s390: crypto: Protect poll timeout update
The poll timeout update via sysfs runs completely unprotected against
other usage sites of the timer. Take the proper lock before fiddling
with the timer.
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Tuchscherer <ingo.tuchscherer@...ibm.com>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: linux-s390@...r.kernel.org
---
P.S: I have serious doubts about the following snippets in that code:
@@ -1174,11 +1174,13 @@ static ssize_t poll_timeout_store(struct
poll_timeout = time;
hr_time = ktime_set(0, poll_timeout);
spin_lock_bh(&ap_poll_timer_lock);
if (!hrtimer_is_queued(&ap_poll_timer) ||
--> !hrtimer_forward(&ap_poll_timer, hrtimer_get_expires
(&ap_poll_timer), hr_time)) {
Why does it check, whether the forwarding resulted in an overrun?
If the timer is not queued, then it is either expired or has never
been started. So if the poll timeout gets written, then the timer is
started when
timer->expires + hr_time < now
This results in random behaviour at best.
hrtimer_set_expires(&ap_poll_timer, hr_time);
hrtimer_start_expires(&ap_poll_timer, HRTIMER_MODE_ABS);
}
@@ -1552,11 +1553,16 @@ static inline void __ap_schedule_poll_timeout
spin_lock_bh(&ap_poll_timer_lock);
if (hrtimer_is_queued(&ap_poll_timer) || ap_suspend_flag)
goto out;
---> if (ktime_to_ns(hrtimer_expires_remaining(&ap_poll_timer)) <= 0) {
The check above does not make any sense either. Again, if the timer is
not queued then it is either expired or was never started. As the
timer is never canceled except on module unload the condition is
always true.
hr_time = ktime_set(0, poll_timeout);
hrtimer_forward_now(&ap_poll_timer, hr_time);
hrtimer_restart(&ap_poll_timer);
}
But that's not scope of that patch and I leave this to the s390
wizards to digest.
---
drivers/s390/crypto/ap_bus.c | 2 ++
1 file changed, 2 insertions(+)
Index: linux/drivers/s390/crypto/ap_bus.c
===================================================================
--- linux.orig/drivers/s390/crypto/ap_bus.c
+++ linux/drivers/s390/crypto/ap_bus.c
@@ -1174,11 +1174,13 @@ static ssize_t poll_timeout_store(struct
poll_timeout = time;
hr_time = ktime_set(0, poll_timeout);
+ spin_lock_bh(&ap_poll_timer_lock);
if (!hrtimer_is_queued(&ap_poll_timer) ||
!hrtimer_forward(&ap_poll_timer, hrtimer_get_expires
(&ap_poll_timer), hr_time)) {
hrtimer_set_expires(&ap_poll_timer, hr_time);
hrtimer_start_expires(&ap_poll_timer,
HRTIMER_MODE_ABS);
}
+ spin_unlock_bh(&ap_poll_timer_lock);
return count;
}
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