Re: [PATCH] MMC: fix hang if card was removed during suspend and unsafe resume was enabled

[Maxim Levitsky <maximlevitsky@gmail.com>]

On Fri, 2010-02-05 at 10:19 -0600, Madhusudhan wrote: 
> 
> > -----Original Message-----
> > From: linux-mmc-owner@vger.kernel.org [mailto:linux-mmc-
> > owner@vger.kernel.org] On Behalf Of Maxim Levitsky
> > Sent: Friday, February 05, 2010 9:52 AM
> > To: Andrew Morton
> > Cc: linux-mmc@vger.kernel.org; Philip Langdale; linux-kernel; Jorg
> > Schummer; linux-pm
> > Subject: Re: [PATCH] MMC: fix hang if card was removed during suspend and
> > unsafe resume was enabled
> > 
> > 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.
> > 
> 
> The assumption with CONFIG_MMC_UNSAFE_RESUME is that the card remains in the
> slot during suspend. The controller driver can simply ignore a card removal
> event if received in the suspended state. Wouldn't that solve your problem?
The assumption is that user doesn't play games with the card while
system is in low power state. Why should my computer hang if I remove
the card and then resume the system?


> 
> The system would resume because of the event and reinsertion of the card
> would enumerate it again.

Don't know about resume on removal, bacause its not supported by most
controllers, and it very very dangerous (Think about closing the lid,
removing the card, and putting the system in a bag....


Best regards,
Maxim Levitsky