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

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Date:	Tue, 16 Feb 2010 11:27:35 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [linux-pm] Is it supposed to be ok to call del_gendisk while
 userspace is frozen?

On Mon, 15 Feb 2010, Rafael J. Wysocki wrote:

> On Monday 15 February 2010, Maxim Levitsky wrote:
> > On Sat, 2010-02-13 at 15:29 +0200, Maxim Levitsky wrote: 
> > > I noticed that currently calling del_gendisk leads to sure deadlock if
> > > attemped from .suspend or .resume functions.
> 
> Well, it shouldn't be called from there, then.

Even if drivers avoid calling it from within suspend methods, they have
to be able to call it from within resume methods.  After all, the
resume method may find that the disk's device has vanished.

> > > Something like that:
> > > 
> > > [<ffffffff8106620a>] ? prepare_to_wait+0x2a/0x90
> > > [<ffffffff810790bd>] ? trace_hardirqs_on+0xd/0x10
> > > [<ffffffff8140db12>] ? _raw_spin_unlock_irqrestore+0x42/0x80
> > > [<ffffffff8112a390>] ? bdi_sched_wait+0x0/0x20
> > > [<ffffffff8112a39e>] bdi_sched_wait+0xe/0x20
> > > [<ffffffff8140af6f>] __wait_on_bit+0x5f/0x90
> > > [<ffffffff8112a390>] ? bdi_sched_wait+0x0/0x20
> > > [<ffffffff8140b018>] out_of_line_wait_on_bit+0x78/0x90
> > > [<ffffffff81065fd0>] ? wake_bit_function+0x0/0x40
> > > [<ffffffff8112a2d3>] ? bdi_queue_work+0xa3/0xe0
> > > [<ffffffff8112a37f>] bdi_sync_writeback+0x6f/0x80
> > > [<ffffffff8112a3d2>] sync_inodes_sb+0x22/0x120
> > > [<ffffffff8112f1d2>] __sync_filesystem+0x82/0x90
> > > [<ffffffff8112f3db>] sync_filesystem+0x4b/0x70
> > > [<ffffffff811391de>] fsync_bdev+0x2e/0x60
> > > [<ffffffff812226be>] invalidate_partition+0x2e/0x50
> > > [<ffffffff8116b92f>] del_gendisk+0x3f/0x140
> > > [<ffffffffa00c0233>] mmc_blk_remove+0x33/0x60 [mmc_block]
> > > [<ffffffff81338977>] mmc_bus_remove+0x17/0x20
> > > [<ffffffff812ce746>] __device_release_driver+0x66/0xc0
> > > [<ffffffff812ce89d>] device_release_driver+0x2d/0x40
> > > [<ffffffff812cd9b5>] bus_remove_device+0xb5/0x120
> > > [<ffffffff812cb46f>] device_del+0x12f/0x1a0
> > > [<ffffffff81338a5b>] mmc_remove_card+0x5b/0x90
> > > [<ffffffff8133ac27>] mmc_sd_remove+0x27/0x50
> > > [<ffffffff81337d8c>] mmc_resume_host+0x10c/0x140
> > > [<ffffffffa00850e9>] sdhci_resume_host+0x69/0xa0 [sdhci]
> > > [<ffffffffa0bdc39e>] sdhci_pci_resume+0x8e/0xb0 [sdhci_pci]
> > > 
> > > bdi_queue_work seems to be the problem.
> > > 
> > > Some device drivers need to remove their cards logically in .suspend,
> > > because the card is removable, and can be changed while system is
> > > suspended.
> 
> I don't know how to resolve this right now.

This is a matter for Jens.  Is the bdi writeback task freezable?  If it
is, should it be made unfreezable?

Alan Stern

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