From: Borislav Petkov <bp@alien8.de>
To: Tejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 25/25] ipc: don't use [delayed_]work_pending()
Date: Tue, 25 Dec 2012 11:46:14 +0100 [thread overview]
Message-ID: <20121225104614.GA7692@liondog.tnic> (raw)
In-Reply-To: <20121225032914.GE10220@mtj.dyndns.org>
On Mon, Dec 24, 2012 at 07:29:14PM -0800, Tejun Heo wrote:
> The behavior is primarily because we want to enable workqueue users
> to guarantee that a full work item execution happens at least once
> after certain event happens. ie. Let's say there's a work item which
> processes data generated by a device. If it's IRQ handler calls
> queue_work() after getting notified of new data segment by the device,
> it would want to guarantee that whole work item execution would happen
> afterwards. If you clear PENDING after execution, the event may
> overlap with the end of the previous execution and the new data won't
> be processed.
Oh, ok, I didn't realize we did some sort of a one-shot queueing - I
thought users of wq are supposed to be polling PENDING and when it is
cleared, they queue. But come to think of it, we can't be doing that in
an IRQ handler.
[ … ]
> It doesn't have anything to do with memory hotplug event itself. It's
> a generic memory access ordering / synchronization issue. There just
> isn't anything preventing test_bit() from seeing PENDING bit from
> before clearing.
That's true. So is it that the whole PENDING bit testing was actually
the wrong sync primitive to use in most cases and we actually really
needed to disable interrupts around testing of that bit?
Which would make your patches actually bugfixes.
/me goes and rereads 0/25 announcement mail.
Yes, it sounds like [delayed_]work_pending() needs to go or at least
needs a big fat comment over it explaining that it is a special, cheaper
alternative to be used *only* in conjunction with other synchronization.
Ok, thanks Tejun, for taking the time and explaining it again to me.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
--
next prev parent reply other threads:[~2012-12-25 10:46 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-22 1:56 [PATCHSET] workqueue: " Tejun Heo
2012-12-22 1:56 ` [PATCH 01/25] charger_manager: " Tejun Heo
2013-01-05 22:11 ` Anton Vorontsov
2012-12-22 1:56 ` [PATCH 02/25] ab8500_charger: " Tejun Heo
[not found] ` <CACRpkdYE3F22rnW+ZRhOWT4VGRhG2CSnb7Rj3gdCosTK8wLQmA@mail.gmail.com>
[not found] ` <50EAA53F.1000304@stericsson.com>
2013-01-07 10:48 ` Arun MURTHY
2013-01-08 14:30 ` Linus Walleij
2012-12-22 1:56 ` [PATCH 03/25] sja1000: " Tejun Heo
2012-12-22 8:01 ` David Miller
2012-12-28 21:40 ` Tejun Heo
2012-12-22 1:56 ` [PATCH 04/25] ipw2x00: simplify scan_event handling Tejun Heo
2013-01-27 21:02 ` Stanislav Yakovlev
2013-02-09 19:31 ` Tejun Heo
2012-12-22 1:56 ` [PATCH 05/25] devfreq: don't use [delayed_]work_pending() Tejun Heo
2012-12-22 1:56 ` [PATCH 06/25] libertas: " Tejun Heo
2012-12-22 1:56 ` [PATCH 07/25] mwifiex: " Tejun Heo
2012-12-22 22:29 ` Bing Zhao
2012-12-28 21:41 ` Tejun Heo
2012-12-22 1:56 ` [PATCH 08/25] thinkpad_acpi: " Tejun Heo
2012-12-22 23:55 ` Henrique de Moraes Holschuh
2012-12-28 21:41 ` Tejun Heo
2012-12-22 1:56 ` [PATCH 09/25] wl1251: " Tejun Heo
2012-12-22 14:14 ` Luciano Coelho
2012-12-28 21:42 ` Tejun Heo
2012-12-22 1:57 ` [PATCH 10/25] kprobes: fix wait_for_kprobe_optimizer() Tejun Heo
2012-12-25 3:51 ` Masami Hiramatsu
2013-01-28 19:49 ` Tejun Heo
2013-01-29 11:53 ` Masami Hiramatsu
2013-02-09 19:33 ` Tejun Heo
2012-12-22 1:57 ` [PATCH 11/25] pm: don't use [delayed_]work_pending() Tejun Heo
2012-12-22 11:53 ` Rafael J. Wysocki
2012-12-25 16:44 ` Tejun Heo
2012-12-22 1:57 ` [PATCH 12/25] bluetooth/l2cap: " Tejun Heo
2013-01-03 22:27 ` Gustavo Padovan
2012-12-22 1:57 ` [PATCH 13/25] sound/wm8350: " Tejun Heo
2012-12-24 16:11 ` Mark Brown
2012-12-22 1:57 ` [PATCH 14/25] rfkill: " Tejun Heo
2012-12-22 20:22 ` Johannes Berg
2012-12-28 21:42 ` Tejun Heo
2012-12-22 1:57 ` [PATCH 15/25] x86/mce: " Tejun Heo
2012-12-25 11:07 ` Borislav Petkov
2012-12-28 21:44 ` [PATCH v2 " Tejun Heo
2012-12-22 1:57 ` [PATCH 16/25] PM / Domains: " Tejun Heo
2012-12-22 11:57 ` Rafael J. Wysocki
2012-12-25 17:03 ` Tejun Heo
2012-12-25 20:33 ` Rafael J. Wysocki
2012-12-26 1:23 ` Tejun Heo
2012-12-22 1:57 ` [PATCH 17/25] wm97xx: " Tejun Heo
2012-12-23 9:54 ` Dmitry Torokhov
2012-12-24 16:18 ` Mark Brown
2013-03-09 23:53 ` Dmitry Torokhov
2013-03-12 18:49 ` Mark Brown
2012-12-24 18:25 ` Tejun Heo
2012-12-22 1:57 ` [PATCH 18/25] TMIO MMC: " Tejun Heo
2012-12-24 22:31 ` Guennadi Liakhovetski
2012-12-22 1:57 ` [PATCH 19/25] net/caif: " Tejun Heo
2012-12-22 1:57 ` [PATCH 20/25] wimax/i2400m: fix i2400m->wake_tx_skb handling Tejun Heo
2012-12-22 15:28 ` Perez-Gonzalez, Inaky
2013-01-04 21:19 ` Dan Williams
2013-02-09 19:35 ` Tejun Heo
2012-12-22 1:57 ` [PATCH 21/25] tty/max3100: don't use [delayed_]work_pending() Tejun Heo
2012-12-22 4:21 ` Greg Kroah-Hartman
2012-12-28 21:44 ` Tejun Heo
2012-12-22 1:57 ` [PATCH 22/25] usb/at91_udc: " Tejun Heo
2013-01-07 16:25 ` Nicolas Ferre
2012-12-22 1:57 ` [PATCH 23/25] video/exynos: " Tejun Heo
2012-12-22 3:05 ` Kukjin Kim
2012-12-26 4:04 ` Jingoo Han
2012-12-28 21:44 ` 'Tejun Heo'
2012-12-22 1:57 ` [PATCH 24/25] debugobjects: " Tejun Heo
2012-12-22 1:57 ` [PATCH 25/25] ipc: " Tejun Heo
2012-12-22 2:15 ` Andrew Morton
2012-12-22 2:22 ` Tejun Heo
2012-12-22 11:09 ` Borislav Petkov
2012-12-24 18:33 ` Tejun Heo
2012-12-24 18:45 ` Tejun Heo
2012-12-24 19:41 ` Borislav Petkov
2012-12-25 3:29 ` Tejun Heo
2012-12-25 10:46 ` Borislav Petkov [this message]
2012-12-25 16:35 ` Tejun Heo
2012-12-24 18:55 ` Borislav Petkov
2012-12-24 19:07 ` Tejun Heo
2012-12-24 19:32 ` Borislav Petkov
2012-12-25 3:18 ` Tejun Heo
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