Re: Mount -o sync regression in 2.6.31

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 13 Nov 2009 14:47:27 -0800
Stephen Hemminger <shemminger@vyatta.com> wrote:

> Okay the scenario is:
> 1. Mount floppy with ext2 filesystem in sync mode
> 2. Write to floppy
> 3. Prematurely eject floppy
> 4. Unmount floppy

I assume that by "prematurely eject", you mean that you waited until
the activity LED had turned off, then hit the button without typing
umount?


Really, I think ext2 is just wrong here.  At unmount time it runs
ext2_sync_super(), which updates a few fields in the superblock and
tries to write them back.

But if the fs was mounted with `-osync' then the driver should be
operating synchronously, dammit!  That means that any time any syscall
alters the filesystem's s_free_blocks_count, s_free_inodes_count or
s_wtime, the driver should write those fields back to the superblock
prior to returning from the syscall.

However that might be unreasonaly anal of us, because those fields
aren't terribly important.  A fsck will whine and fix them up.

> This triggers this warning in 2.6.31 which did not occur in 2.6.30

hm, I wonder why that changed.  The warning's been there for a while.

>  [  580.325447] floppy0: disk absent or changed during operation
>  [  580.325454] lost page write due to I/O error on fd0
>  [  580.958434] ------------[ cut here ]------------
>  [  580.958437] WARNING: at fs/buffer.c:1152 mark_buffer_dirty+0x23/0x7d()
>  [  580.958440] Hardware name: System Product Name
>  [  580.958442] Modules linked in: hid_belkin binfmt_misc bridge stp llc kvm_intel kvm ipv6 video output pci_slot acpi_cpufreq cpufreq_powersave cpufreq_ondemand cpufreq_conservative cpufreq_userspace psmouse pcspkr serio_raw rtc_cmos wmi evdev sg sr_mod cdrom usbhid mvsas pata_acpi pata_marvell ata_piix libsas ahci igb sky2 scsi_transport_sas dca e1000e floppy dm_mirror dm_region_hash dm_log dm_snapshot dm_mod fuse
>  [  580.958475] Pid: 8340, comm: umount Not tainted 2.6.30-rc6-bisect #12
>  [  580.958477] Call Trace:
>  [  580.958483]  [<ffffffff80232ebb>] ? warn_slowpath_fmt+0xd9/0x10b
>  [  580.958489]  [<ffffffff80270031>] ? find_get_pages_tag+0x41/0xdd
>  [  580.958494]  [<ffffffff802782f0>] ? pagevec_lookup+0x17/0x1e
>  [  580.958498]  [<ffffffff80279377>] ? truncate_inode_pages_range+0x21d/0x31d
>  [  580.958502]  [<ffffffff80270db5>] ? wait_on_page_writeback_range+0xce/0x11b
>  [  580.958507]  [<ffffffff80245037>] ? bit_waitqueue+0x10/0xa0
>  [  580.958510]  [<ffffffff802be80d>] ? mark_buffer_dirty+0x23/0x7d
>  [  580.958515]  [<ffffffff803003eb>] ? ext2_sync_super+0x39/0x55
>  [  580.958519]  [<ffffffff8030079c>] ? ext2_put_super+0x34/0xc7
>  [  580.958524]  [<ffffffff802a3174>] ? generic_shutdown_super+0x70/0xfd
>  [  580.958533]  [<ffffffff802a3223>] ? kill_block_super+0x22/0x3a
>  [  580.958537]  [<ffffffff802a3831>] ? deactivate_super+0x43/0x5a
>  [  580.958541]  [<ffffffff802b56f9>] ? sys_umount+0x2d8/0x307
>  [  580.958546]  [<ffffffff8020aeeb>] ? system_call_fastpath+0x16/0x1b
>  [  580.958549] ---[ end trace ccbde6411acd243f ]---
>  [  580.958580] floppy0: disk absent or changed during operation
>  [  580.958587] lost page write due to I/O error on fd0

	void mark_buffer_dirty(struct buffer_head *bh)
	{
		WARN_ON_ONCE(!buffer_uptodate(bh));

that's expected, I expect.  And it's just a WARN_ON_ONCE() so it
won't be flooding logs.  We could just delete it I suppose.

> Bisecting between 2.6.30 and 2.6.31-rc1 reduced it down to:
> 
> 8f184f27300f66f6dcc8296c2dae7a1fbe8429c9 is first bad commit
> commit 8f184f27300f66f6dcc8296c2dae7a1fbe8429c9
> Author: Frederic Weisbecker <fweisbec@gmail.com>
> Date:   Sat May 16 06:24:36 2009 +0200
> 
>     tracing/stat: replace linked list by an rbtree for sorting

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