From: Arjan van de Ven <arjan@linux.intel.com>
To: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Ming Lei <ming.lei@canonical.com>,
Alex Riesen <raa.lkml@gmail.com>,
Alan Stern <stern@rowland.harvard.edu>,
Jens Axboe <axboe@kernel.dk>,
USB list <linux-usb@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: USB device cannot be reconnected and khubd "blocked for more than 120 seconds"
Date: Tue, 15 Jan 2013 16:25:54 -0800 [thread overview]
Message-ID: <50F5F392.7010709@linux.intel.com> (raw)
In-Reply-To: <20130115235043.GJ2668@htj.dyndns.org>
> For now, I'm gonna implement simple "I'm not gonna wait for myself"
> self-deadlock avoidance. If this needs any more sophistication, I
> think we better reimplement it so that we can explicitly match up and
> track who's gonna wait for what instead of throwing everything into a
> single cookie space and then try to work back from there.
async fundamentally had the concept of a monotonic increasing number,
and that you could always wait for "everyone before me".
then people (like me) wanted exceptions to what "everyone" means ;-(
I'm ok with going back to a single space and simplify the world.
the case with (usb) module loading is "fun"...
people expect the device to be there (since frankly, it's hard to do otherwise)..
... but it's also really hard due to the nature of USB.. USB is async in nature,
even independent of the kernel async stuff.
Example: Load ehci.ko ... the actual use devices don't show up for some time.
the module wait case is tricky, and I wonder if there's deadlocks lurking even without async.
(btw there is a similar situation at the end of the normal kernel boot versus things like asynchronous
driver initializing... but we "skip" that in the case of an initrd is used to bypass a very similar deadlock.
this is even without "async" in use.. typical hard case is the PS/2 mouse probing)
at some point in the past we had the concept of "request a module but don't wait for it",
and I wonder if that is what should have been used here.
Doing a "range wait", with the start of the range being taken at the start of module loading
is a bit of a hack, but it'll work for the userspace expected semantics of all async stuff of
the *loaded module* be done, independent of all other modules/async stuff.
It's not as deadlocky as one might think, but it's not going to be efficient to implement.
not self-deadlocking likely solves most practical cases though
next prev parent reply other threads:[~2013-01-16 0:27 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-11 21:04 USB device cannot be reconnected and khubd "blocked for more than 120 seconds" Alex Riesen
2013-01-12 7:48 ` Alex Riesen
2013-01-12 9:18 ` Lan Tianyu
2013-01-12 17:37 ` Alan Stern
2013-01-12 19:39 ` Alex Riesen
2013-01-12 20:33 ` Alex Riesen
2013-01-12 22:52 ` Alan Stern
2013-01-13 12:09 ` Alex Riesen
2013-01-13 16:56 ` Alan Stern
2013-01-13 17:42 ` Alex Riesen
2013-01-13 19:16 ` Oliver Neukum
2013-01-14 2:39 ` Alan Stern
2013-01-14 16:43 ` Alex Riesen
2013-01-14 3:47 ` Ming Lei
2013-01-14 7:15 ` Ming Lei
2013-01-14 17:30 ` Linus Torvalds
2013-01-14 18:04 ` Alan Stern
2013-01-14 18:34 ` Linus Torvalds
2013-01-15 1:53 ` Ming Lei
2013-01-15 6:23 ` Ming Lei
2013-01-15 17:36 ` Linus Torvalds
2013-01-15 18:18 ` Linus Torvalds
2013-01-15 23:17 ` Tejun Heo
2013-01-15 18:20 ` Alan Stern
2013-01-15 18:39 ` Tejun Heo
2013-01-15 18:32 ` Tejun Heo
2013-01-15 20:18 ` Linus Torvalds
2013-01-15 23:50 ` Tejun Heo
2013-01-16 0:25 ` Arjan van de Ven [this message]
2013-01-16 0:35 ` Tejun Heo
2013-01-16 4:01 ` Alan Stern
2013-01-16 16:12 ` Tejun Heo
2013-01-16 17:01 ` Alan Stern
2013-01-16 17:37 ` Tejun Heo
2013-01-16 17:51 ` Alan Stern
2013-01-16 0:36 ` Linus Torvalds
2013-01-16 0:40 ` Linus Torvalds
2013-01-16 2:52 ` [PATCH] module, async: async_synchronize_full() on module init iff async is used Tejun Heo
2013-01-16 3:00 ` Linus Torvalds
2013-01-16 3:25 ` Tejun Heo
2013-01-16 3:37 ` Linus Torvalds
2013-01-16 16:22 ` Arjan van de Ven
2013-01-16 16:48 ` Tejun Heo
2013-01-16 17:03 ` Arjan van de Ven
2013-01-16 17:06 ` Linus Torvalds
2013-01-16 21:30 ` [PATCH 1/2] init, block: try to load default elevator module early during boot Tejun Heo
2013-01-17 18:05 ` Linus Torvalds
2013-01-17 18:38 ` Tejun Heo
2013-01-17 18:46 ` Linus Torvalds
2013-01-17 18:59 ` Tejun Heo
2013-01-17 19:00 ` Linus Torvalds
2013-01-18 1:24 ` [PATCH 1/3] workqueue: set PF_WQ_WORKER on rescuers Tejun Heo
2013-01-18 1:25 ` [PATCH 2/3] workqueue, async: implement work/async_current_func() Tejun Heo
2013-01-18 2:47 ` Linus Torvalds
2013-01-18 2:59 ` Tejun Heo
2013-01-18 3:04 ` Tejun Heo
2013-01-18 3:18 ` Linus Torvalds
2013-01-18 3:47 ` Tejun Heo
2013-01-18 22:08 ` [PATCH 1/5] workqueue: set PF_WQ_WORKER on rescuers Tejun Heo
2013-01-18 22:10 ` [PATCH 2/5] workqueue: rename kernel/workqueue_sched.h to kernel/workqueue_internal.h Tejun Heo
2013-01-18 22:11 ` [PATCH 3/5] workqueue: move struct worker definition to workqueue_internal.h Tejun Heo
2013-01-18 22:11 ` [PATCH 4/5] workqueue: implement current_is_async() Tejun Heo
2013-01-18 22:12 ` [PATCH 5/5] async, kmod: warn on synchronous request_module() from async workers Tejun Heo
2022-06-23 5:25 ` Saravana Kannan
2013-01-18 1:27 ` [PATCH 3/3] " Tejun Heo
2013-01-23 0:53 ` [PATCH v2 1/2] init, block: try to load default elevator module early during boot Tejun Heo
2013-01-16 21:31 ` [PATCH 2/2] block: don't request module during elevator init Tejun Heo
2013-01-23 0:51 ` [PATCH v2 " Tejun Heo
2013-01-16 3:30 ` [PATCH] module, async: async_synchronize_full() on module init iff async is used Ming Lei
2013-01-16 4:24 ` Rusty Russell
2013-01-16 11:36 ` Alex Riesen
2013-08-12 7:04 ` [3.8-rc3 -> 3.8-rc4 regression] " Jonathan Nieder
2013-08-12 15:09 ` Tejun Heo
2013-11-26 21:29 ` Josh Hunt
2013-11-26 21:53 ` Linus Torvalds
2013-11-26 22:12 ` Josh Hunt
2013-11-26 22:29 ` Tejun Heo
2013-12-03 14:28 ` Josh Hunt
2013-12-03 15:19 ` Tejun Heo
2013-12-04 23:01 ` Josh Hunt
2013-12-04 23:12 ` Tejun Heo
2013-11-26 22:30 ` Linus Torvalds
2013-01-16 0:44 ` USB device cannot be reconnected and khubd "blocked for more than 120 seconds" Tejun Heo
2013-01-16 17:19 ` [PATCH] async: fix __lowest_in_progress() Tejun Heo
2013-01-17 18:16 ` Linus Torvalds
2013-01-17 18:50 ` Tejun Heo
2013-01-23 0:15 ` [PATCH v2] " Tejun Heo
2013-01-23 0:22 ` Linus Torvalds
2013-01-16 3:05 ` USB device cannot be reconnected and khubd "blocked for more than 120 seconds" Ming Lei
2013-01-16 4:14 ` Linus Torvalds
2013-01-14 8:22 ` Oliver Neukum
2013-01-14 8:40 ` Ming Lei
2013-01-12 19:56 ` Alex Riesen
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