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Re: [PATCH RESEND] xfs: fix assertion failure in xfs_vm_write_failed()

To: Jeff Liu <jeff.liu@xxxxxxxxxx>
Subject: Re: [PATCH RESEND] xfs: fix assertion failure in xfs_vm_write_failed()
From: Ben Myers <bpm@xxxxxxx>
Date: Fri, 19 Jul 2013 14:02:20 -0500
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <51E4D5F4.902@xxxxxxxxxx>
References: <51E4D5F4.902@xxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
Jeff, 

On Tue, Jul 16, 2013 at 01:11:16PM +0800, Jeff Liu wrote:
> From: Jie Liu <jeff.liu@xxxxxxxxxx>
> 
> In xfs_vm_write_failed(), we evaluate the block_offset of pos with
> PAGE_MASK which is an unsigned long.  That is fine on 64-bit platforms
> regardless of whether the request pos is 32-bit or 64-bit.  However, on
> 32-bit platforms the value is 0xfffff000 and so the high 32 bits in it
> will be masked off with (pos & PAGE_MASK) for a 64-bit pos.
> 
> As a result, the evaluated block_offset is incorrect which will cause
> this failure ASSERT(block_offset + from == pos); and potentially pass
> the wrong block to xfs_vm_kill_delalloc_range().
> 
> In this case, we can get a kernel panic if CONFIG_XFS_DEBUG is enabled:
> 
> XFS: Assertion failed: block_offset + from == pos, file: fs/xfs/xfs_aops.c, 
> line: 1504
> 
> ------------[ cut here ]------------
>  kernel BUG at fs/xfs/xfs_message.c:100!
>  invalid opcode: 0000 [#1] SMP
>  ........
>  Pid: 4057, comm: mkfs.xfs Tainted: G           O 3.9.0-rc2 #1
>  EIP: 0060:[<f94a7e8b>] EFLAGS: 00010282 CPU: 0
>  EIP is at assfail+0x2b/0x30 [xfs]
>  EAX: 00000056 EBX: f6ef28a0 ECX: 00000007 EDX: f57d22a4
>  ESI: 1c2fb000 EDI: 00000000 EBP: ea6b5d30 ESP: ea6b5d1c
>  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
>  CR0: 8005003b CR2: 094f3ff4 CR3: 2bcb4000 CR4: 000006f0
>  DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
>  DR6: ffff0ff0 DR7: 00000400
>  Process mkfs.xfs (pid: 4057, ti=ea6b4000 task=ea5799e0 task.ti=ea6b4000)
>  Stack:
>  00000000 f9525c48 f951fa80 f951f96b 000005e4 ea6b5d7c f9494b34 c19b0ea2
>  00000066 f3d6c620 c19b0ea2 00000000 e9a91458 00001000 00000000 00000000
>  00000000 c15c7e89 00000000 1c2fb000 00000000 00000000 1c2fb000 00000080
>  Call Trace:
>  [<f9494b34>] xfs_vm_write_failed+0x74/0x1b0 [xfs]
>  [<c15c7e89>] ? printk+0x4d/0x4f
>  [<f9494d7d>] xfs_vm_write_begin+0x10d/0x170 [xfs]
>  [<c110a34c>] generic_file_buffered_write+0xdc/0x210
>  [<f949b669>] xfs_file_buffered_aio_write+0xf9/0x190 [xfs]
>  [<f949b7f3>] xfs_file_aio_write+0xf3/0x160 [xfs]
>  [<c115e504>] do_sync_write+0x94/0xd0
>  [<c115ed1f>] vfs_write+0x8f/0x160
>  [<c115e470>] ? wait_on_retry_sync_kiocb+0x50/0x50
>  [<c115f017>] sys_write+0x47/0x80
>  [<c15d860d>] sysenter_do_call+0x12/0x28
>  .............
>  EIP: [<f94a7e8b>] assfail+0x2b/0x30 [xfs] SS:ESP 0068:ea6b5d1c
>  ---[ end trace cdd9af4f4ecab42f ]---
>  Kernel panic - not syncing: Fatal exception
> 
> In order to avoid this, we can evaluate the block_offset of the start
> of the page by using shifts rather than masks the mismatch problem.
> 
> Thanks Dave Chinner for help finding and fixing this bug.
> 
> Reported-by: Michael L. Semon <mlsemon35@xxxxxxxxx>
> Reviewed-by: Dave Chinner <david@xxxxxxxxxxxxx>
> Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>
> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>

Applied.

Thanks,
        Ben

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