linux-kernel - Re: [linux-pm] Is it supposed to be ok to call del

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Date:	Thu, 13 May 2010 14:44:26 -0700
From:	Matt Reimer <mattjreimer@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>
Subject: Re: [linux-pm] Is it supposed to be ok to call del_gendisk while 
	userspace is frozen?

On Wed, May 12, 2010 at 7:50 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Tue, 11 May 2010, Matt Reimer wrote:
>
>> >> or has a consensus about how to fix this been
>> >> achieved? I'm hitting the same problem and have some time to work on a
>> >> fix.
>> >
>> > Generally, it looks like del_gendisk should thaw writeback threads, but not
>> > during suspend, only during resume.
>>
>> Thawing the writeback thread only during resume does fix the case
>> Maxim originally presented:
>>
>> 0. build kernel with CONFIG_MMC_UNSAFE_RESUME
>> 1. insert SD card
>> 2. suspend
>> 3. remove SD card while suspended
>> 4. resume from suspend hangs
>>
>> But if CONFIG_MMC_UNSAFE_RESUME is not set, the kernel oopses during
>> suspend because the MMC device suspend times out:
>>
>> mmc0: card e624 removed
>> **** DPM device timeout: pxa2xx-mci.0 (pxa2xx-mci)
>> kernel BUG at /home/mreimer/sdg/android/android-2.1/kernel/drivers/base/power/main.c:453!
>> Unable to handle kernel NULL pointer dereference at virtual address 00000000
>> pgd = c0004000
>> [00000000] *pgd=00000000
>> Internal error: Oops: 817 [#1] PREEMPT
>>
>> If I thaw the writeback thread unconditionally in del_gendisk() then
>> suspend and resume work as expected for both CONFIG_MMC_UNSAFE_RESUME
>> set/not set, even when the card is removed while suspended.
>>
>> So what is the proper fix?
>
> I don't see any reason not to let del_gendisk thaw the writeback thread
> during suspend.  Since the device is going away anyhow, letting the
> thread run shouldn't cause any problems.

So how does the attached patch look?

Matt


>From 20d8340471eb05aa54af1349f4ddccecd9c230c6 Mon Sep 17 00:00:00 2001
From: Matt Reimer <mreimer@...systems.com>
Date: Thu, 13 May 2010 14:36:54 -0700
Subject: [PATCH] fs: prevent hang on suspend/resume when MMC/SD card present

Devices can come and go from the MMC/SD bus during suspend or resume,
when the writeback thread is frozen, resulting in a hang. So thaw the
writeback thread in del_gendisk() to prevent the hang.

Signed-off-by: Matt Reimer <mreimer@...systems.com>
---
 fs/partitions/check.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/fs/partitions/check.c b/fs/partitions/check.c
index e238ab2..b303919 100644
--- a/fs/partitions/check.c
+++ b/fs/partitions/check.c
@@ -666,6 +666,8 @@ void del_gendisk(struct gendisk *disk)
        struct disk_part_iter piter;
        struct hd_struct *part;

+       thaw_process(disk->queue->backing_dev_info.wb.task);
+
        /* invalidate stuff */
        disk_part_iter_init(&piter, disk,
                             DISK_PITER_INCL_EMPTY | DISK_PITER_REVERSE);
-- 
1.7.0.4

Download attachment "0001-fs-prevent-hang-on-suspend-resume-when-MMC-SD-card-p.patch" of type "application/octet-stream" (1014 bytes)