linux-kernel - Re: [PATCH] module, async: async_synchronize_full() on module init iff async is used

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Date:	Wed, 16 Jan 2013 12:36:27 +0100
From:	Alex Riesen <raa.lkml@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ming Lei <ming.lei@...onical.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Jens Axboe <axboe@...nel.dk>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] module, async: async_synchronize_full() on module init
 iff async is used

On Wed, Jan 16, 2013 at 3:52 AM, Tejun Heo <tj@...nel.org> wrote:
> This avoids the described deadlock because iosched module doesn't use
> async and thus wouldn't invoke async_synchronize_full().  This is
> hacky and incomplete.  It will deadlock if async module loading nests;
> however, this works around the known problem case and seems to be the
> best of bad options.

I confirm it fixes the original problem.

Tested-by: Alex Riesen <raa.lkml@...il.com>

[   27.594951] hub 1-1:1.0: state 7 ports 6 chg 0000 evt 0004
[   27.595245] hub 1-1:1.0: port 2, status 0101, change 0001, 12 Mb/s
[   27.698995] hub 1-1:1.0: debounce: port 2: total 100ms stable 100ms
status 0x101
[   27.709977] hub 1-1:1.0: port 2 not reset yet, waiting 10ms
[   27.771888] usb 1-1.2: new high-speed USB device number 3 using ehci-pci
[   27.782871] hub 1-1:1.0: port 2 not reset yet, waiting 10ms
[   27.857503] usb 1-1.2: default language 0x0409
[   27.858248] usb 1-1.2: udev 3, busnum 1, minor = 2
[   27.858258] usb 1-1.2: New USB device found, idVendor=0781, idProduct=5408
[   27.858263] usb 1-1.2: New USB device strings: Mfr=1, Product=2,
SerialNumber=3
[   27.858267] usb 1-1.2: Product: U3 Titanium
[   27.858271] usb 1-1.2: Manufacturer: SanDisk Corporation
[   27.858275] usb 1-1.2: SerialNumber: 0000187A3A60F1E9
[   27.858800] usb 1-1.2: usb_probe_device
[   27.858815] usb 1-1.2: configuration #1 chosen from 1 choice
[   27.858940] usb 1-1.2: adding 1-1.2:1.0 (config #1, interface 0)
[   27.859246] usb-storage 1-1.2:1.0: usb_probe_interface
[   27.859258] usb-storage 1-1.2:1.0: usb_probe_interface - got id
[   27.859516] scsi6 : usb-storage 1-1.2:1.0
[   28.865771] io scheduler deadline registered (default)
[   28.866705] scsi 6:0:0:0: Direct-Access     SanDisk  U3 Titanium
  2.18 PQ: 0 ANSI: 2
[   28.869483] sd 6:0:0:0: Attached scsi generic sg1 type 0
[   28.869700] sd 6:0:0:0: [sdb] 4013713 512-byte logical blocks:
(2.05 GB/1.91 GiB)
[   28.870197] sd 6:0:0:0: [sdb] Write Protect is off
[   28.870204] sd 6:0:0:0: [sdb] Mode Sense: 03 00 00 00
[   28.870692] sd 6:0:0:0: [sdb] No Caching mode page present
[   28.870697] sd 6:0:0:0: [sdb] Assuming drive cache: write through
[   28.873565] sd 6:0:0:0: [sdb] No Caching mode page present
[   28.873575] sd 6:0:0:0: [sdb] Assuming drive cache: write through
[   28.883895]  sdb: sdb1
[   28.887775] sd 6:0:0:0: [sdb] No Caching mode page present
[   28.887783] sd 6:0:0:0: [sdb] Assuming drive cache: write through
[   28.887789] sd 6:0:0:0: [sdb] Attached SCSI removable disk

The filesystem can be mounted and files can be read.
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