From: Alan Stern <stern@rowland.harvard.edu>
To: Peter Chen <hzpeterchen@gmail.com>
Cc: tj@kernel.org, <florian@mickler.org>, <linux-usb@vger.kernel.org>,
<linux-kernel@vger.kernel.org>,
<usb-storage@lists.one-eyed-alien.net>
Subject: Re: Freezable workqueue blocks non-freezable workqueue during the system resume process
Date: Tue, 23 Feb 2016 10:34:09 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1602231024360.1698-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20160223032056.GB12256@shlinux2.ap.freescale.net>
On Tue, 23 Feb 2016, Peter Chen wrote:
> Hi Tejun Heo and Florian Mickler,
>
> I have a question that during the system resume process, the freezable
> workqueue can be thawed if there is a non-freezable workqueue is
> blocked (At uninterruptable state)?
>
> My case like below, I have a USB OTG (Micro-AB) cable is at USB
> Micro-B port, and there is a USB driver on it, and un-plug this
> cable can wake up system from the suspend. There is a non-freezable
> workqueue ci_otg will be scheduled after disconnecting OTG cable,
> and in its worker ci_otg_work, it will try to disconnect USB drive,
> and flush disk information.
These operations probably are not safe while the system is resuming.
It might be best to make them wait until the resume is finished.
> But flush disk information is done by
> freezable workqueue writeback, it seeems workqueue writeback is
> never got chance to execute, the workqueue ci_otg is waiting there
> forever, and the system is deadlock.
> Both change workqueue ci_otg as freezable or change workqueue writeback
> as non-freezable can fix this problem.
It sounds like making ci_otg freezable is the easiest solution.
> Please ignore it, the system is locked at driver's resume,
> maybe at scsi or usb driver, so of cos, the freezable processes
> can't be thawed.
> > [ 555.263177] [<c0043b1c>] (flush_work) from [<c0043fac>] (flush_delayed_work+0x48/0x4c)
> > [ 555.271106] r8:ed5b5000 r7:c0b38a3c r6:eea439cc r5:eea4372c r4:eea4372c
> > [ 555.277958] [<c0043f64>] (flush_delayed_work) from [<c00eae18>] (bdi_unregister+0x84/0xec)
> > [ 555.286236] r4:eea43520 r3:20000153
> > [ 555.289885] [<c00ead94>] (bdi_unregister) from [<c02c2154>] (blk_cleanup_queue+0x180/0x29c)
> > [ 555.298250] r5:eea43808 r4:eea43400
You might want to complain to the block-layer people about this. I
don't know if anything can be done to fix it.
Or maybe flush_work and flush_delayed_work can be changed to avoid
blocking if the workqueue is frozen. Tejun?
Alan Stern
next prev parent reply other threads:[~2016-02-23 15:34 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-23 3:20 Freezable workqueue blocks non-freezable workqueue during the system resume process Peter Chen
2016-02-23 9:47 ` Peter Chen
2016-02-23 15:34 ` Alan Stern [this message]
2016-02-24 7:24 ` Peter Chen
2016-02-25 22:01 ` Tejun Heo
2016-02-26 6:19 ` Peter Chen
2016-03-02 16:00 ` Tejun Heo
2016-03-03 9:33 ` Jan Kara
2016-03-11 17:56 ` Tejun Heo
2016-03-14 7:22 ` Jan Kara
2016-03-14 14:37 ` Alan Stern
2016-03-15 9:25 ` Jan Kara
2016-03-16 15:00 ` Tejun Heo
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