From: Thomas Gleixner <tglx@linutronix.de>
To: Finn Thain <fthain@telegraphics.com.au>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Arnd Bergmann <arnd@arndb.de>,
Stephen N Chivers <schivers@csc.com.au>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
John Stultz <john.stultz@linaro.org>,
linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource APIy
Date: Sun, 18 Nov 2018 18:12:46 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.21.1811181759330.9459@nanos.tec.linutronix.de> (raw)
In-Reply-To: <alpine.LNX.2.21.1811140925270.371@nippy.intranet>
Finn,
On Wed, 14 Nov 2018, Finn Thain wrote:
> On Tue, 13 Nov 2018, Thomas Gleixner wrote:
> > Urgh. Then you have more serious trouble. If the interrupting handler
> > calls any of the time accessor functions then you can actually live lock
> > when the interrupt happens in the middle of the write locked section of
> > the core timekeeping update.
>
> Does this apply to arch_gettimeoffset also? If so, that would mean another
> bug fix patch for -stable...
arch_gettimeoffset() can be called from any context. The only interrupt
which can affect it is the timer interrupt. As m68k are all UP machines
this is not a problem because:
ktime_get()
do {
seq = read_seqcount_begin(tk.seq);
nsec = .... + arch_gettimeoffset();
} while (seqcount_retry(tk.seq);
and the timer interrupt does:
arch_timeoffset += value;
...
xtime_update()
...
write_seqcount_begin(tk.seq);
....
write_seqcount_end(tk.seq);
So where ever the timer interrupt hits inside of ktime_get() or any other
accessor the seqcount will make it retry, so the result is always
consistent.
For SMP that would be a different story.
> > So you really want to disable interrupts across the whole timer
> > interrupt function or make sure that the timer interrupt is the highest
> > priority one on the system.
> >
>
> The timer interrupt priority isn't always what one would hope.
>
> But I can certainly disable interrupts for timer_interrupt() execution
> (that is, xtime_update() etc.)
Oh yes, you should.
Thanks,
tglx
next prev parent reply other threads:[~2018-11-18 17:12 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-12 4:12 [RFC PATCH 00/13] m68k: Drop arch_gettimeoffset and adopt clocksource API Finn Thain
2018-11-12 4:12 ` [RFC PATCH 08/13] m68k: atari: Convert to " Finn Thain
2018-11-12 4:12 ` [RFC PATCH 04/13] m68k: mac: Clean up unused timer definitions Finn Thain
2018-11-12 4:12 ` [RFC PATCH 10/13] m68k: hp300: Convert to clocksource API Finn Thain
2018-11-12 4:12 ` [RFC PATCH 11/13] m68k: mac: " Finn Thain
2018-11-12 4:12 ` [RFC PATCH 01/13] arm: Fix mutual exclusion in arch_gettimeoffset Finn Thain
2018-11-12 8:34 ` Christoph Hellwig
2018-11-13 3:39 ` Finn Thain
2018-11-13 9:20 ` Russell King - ARM Linux
2018-11-13 21:55 ` Finn Thain
2018-11-13 23:43 ` Russell King - ARM Linux
2018-11-14 1:35 ` Michael Schmitz
2018-11-14 7:58 ` Russell King - ARM Linux
2018-11-15 1:34 ` Michael Schmitz
2018-11-14 3:17 ` Finn Thain
2018-11-14 14:16 ` Russell King - ARM Linux
2018-11-14 14:58 ` Geert Uytterhoeven
2018-11-14 18:11 ` Russell King - ARM Linux
2018-11-15 4:12 ` Finn Thain
2018-11-16 17:47 ` Russell King - ARM Linux
2018-11-16 22:49 ` Finn Thain
2018-11-17 3:00 ` Michael Schmitz
2018-11-14 12:05 ` Russell King - ARM Linux
2018-11-12 4:12 ` [RFC PATCH 02/13] m68k: " Finn Thain
2018-11-12 4:12 ` [RFC PATCH 07/13] m68k: amiga: Convert to clocksource API Finn Thain
2018-11-12 9:02 ` Geert Uytterhoeven
2018-11-12 9:21 ` Finn Thain
2018-11-12 4:12 ` [RFC PATCH 09/13] m68k: bvme6000: " Finn Thain
2018-11-12 4:12 ` [RFC PATCH 06/13] m68k: Drop ARCH_USES_GETTIMEOFFSET Finn Thain
2018-11-12 9:00 ` Geert Uytterhoeven
2018-11-12 9:06 ` Finn Thain
2018-11-13 2:29 ` Michael Schmitz
2018-11-13 3:14 ` Finn Thain
2018-11-13 4:50 ` Michael Schmitz
2018-11-13 6:15 ` Finn Thain
2018-11-13 8:24 ` Michael Schmitz
2018-11-13 22:11 ` Finn Thain
2018-11-14 1:08 ` Michael Schmitz
2018-11-14 2:58 ` Michael Schmitz
2018-11-14 23:54 ` Michael Schmitz
2018-11-15 4:37 ` Finn Thain
2018-11-15 6:35 ` Michael Schmitz
2018-11-16 0:04 ` Finn Thain
2018-11-12 4:12 ` [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource API Finn Thain
2018-11-12 18:37 ` Thomas Gleixner
2018-11-13 0:11 ` Finn Thain
2018-11-13 22:04 ` Finn Thain
2018-11-13 22:10 ` [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource APIy Thomas Gleixner
2018-11-13 22:33 ` Finn Thain
2018-11-18 17:12 ` Thomas Gleixner [this message]
2018-11-12 4:12 ` [RFC PATCH 03/13] m68k: mac: Fix VIA timer counter accesses Finn Thain
2018-11-12 4:12 ` [RFC PATCH 12/13] m68k: mvme147: Convert to clocksource API Finn Thain
2018-11-12 4:12 ` [RFC PATCH 05/13] m68k: apollo, q40, sun3, sun3x: Remove arch_gettimeoffset implementations Finn Thain
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