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Subject: Re: [PATCH] MMC: fix hang if card was removed during suspend and
 unsafe resume was enabled
From: Maxim Levitsky <maximlevitsky@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mmc@vger.kernel.org, Philip Langdale <philipl@overt.org>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Jorg Schummer <ext-jorg.2.schummer@nokia.com>,
       linux-pm <linux-pm@lists.linux-foundation.org>
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Date: Fri, 05 Feb 2010 17:52:00 +0200
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On Fri, 2010-02-05 at 06:39 -0800, Andrew Morton wrote: 
> On Fri, 05 Feb 2010 16:19:20 +0200 Maxim Levitsky <maximlevitsky@gmail.com> wrote:
> 
> > > 
> > > There is no del_disk in the kernel.  Let's be more specific (and
> > > accurate!) about the hang.  I assume it's
> > > mmc_remove_card->device_del->kobject_uevent?
> > Sorry!
> > I was referring to del_gendisk. 
> > 
> > <4>[15241.042047]  [<ffffffff8106620a>] ? prepare_to_wait+0x2a/0x90
> > <4>[15241.042159]  [<ffffffff810790bd>] ? trace_hardirqs_on+0xd/0x10
> > <4>[15241.042271]  [<ffffffff8140db12>] ? _raw_spin_unlock_irqrestore+0x42/0x80
> > <4>[15241.042386]  [<ffffffff8112a390>] ? bdi_sched_wait+0x0/0x20
> > <4>[15241.042496]  [<ffffffff8112a39e>] bdi_sched_wait+0xe/0x20
> > <4>[15241.042606]  [<ffffffff8140af6f>] __wait_on_bit+0x5f/0x90
> > <4>[15241.042714]  [<ffffffff8112a390>] ? bdi_sched_wait+0x0/0x20
> > <4>[15241.042824]  [<ffffffff8140b018>] out_of_line_wait_on_bit+0x78/0x90
> > <4>[15241.042935]  [<ffffffff81065fd0>] ? wake_bit_function+0x0/0x40
> > <4>[15241.043045]  [<ffffffff8112a2d3>] ? bdi_queue_work+0xa3/0xe0
> > <4>[15241.043155]  [<ffffffff8112a37f>] bdi_sync_writeback+0x6f/0x80
> > <4>[15241.043265]  [<ffffffff8112a3d2>] sync_inodes_sb+0x22/0x120
> > <4>[15241.043375]  [<ffffffff8112f1d2>] __sync_filesystem+0x82/0x90
> > <4>[15241.043485]  [<ffffffff8112f3db>] sync_filesystem+0x4b/0x70
> > <4>[15241.043594]  [<ffffffff811391de>] fsync_bdev+0x2e/0x60
> > <4>[15241.043704]  [<ffffffff812226be>] invalidate_partition+0x2e/0x50
> > <4>[15241.043816]  [<ffffffff8116b92f>] del_gendisk+0x3f/0x140
> > <4>[15241.043926]  [<ffffffffa00c0233>] mmc_blk_remove+0x33/0x60 [mmc_block]
> > <4>[15241.044043]  [<ffffffff81338977>] mmc_bus_remove+0x17/0x20
> > <4>[15241.044152]  [<ffffffff812ce746>] __device_release_driver+0x66/0xc0
> > <4>[15241.044264]  [<ffffffff812ce89d>] device_release_driver+0x2d/0x40
> > <4>[15241.044375]  [<ffffffff812cd9b5>] bus_remove_device+0xb5/0x120
> > <4>[15241.044486]  [<ffffffff812cb46f>] device_del+0x12f/0x1a0
> > <4>[15241.044593]  [<ffffffff81338a5b>] mmc_remove_card+0x5b/0x90
> > <4>[15241.044702]  [<ffffffff8133ac27>] mmc_sd_remove+0x27/0x50
> > <4>[15241.044811]  [<ffffffff81337d8c>] mmc_resume_host+0x10c/0x140
> > <4>[15241.044929]  [<ffffffffa00850e9>] sdhci_resume_host+0x69/0xa0 [sdhci]
> > <4>[15241.045044]  [<ffffffffa0bdc39e>] sdhci_pci_resume+0x8e/0xb0 [sdhci_pci]
> 
> So what's the hang?  del_gendisk is doing IO?  I'd assumed that it was
> because it was calling kobject_uevent, but userspace is frozen.

This is a backtrace of a hang.

The patch I sent tries not to remove the card during suspend, by letting
card presence logic to run after system is fully resumed.

However if CONFIG_MMC_UNSAFE_RESUME is not set, card would be removed at
suspend time, again with userspace frozen.
I will need to add some knobs to remove and add (if present) the card
when system is fully resumed. It is possible, but I will need to dig the
mmc code a bit deeper.

What I suggested is make del_gendisk suspend safe somehow.

Best regards,
Maxim Levitsky

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