Re: use-after-free on log replay failure

Alex Lyakas
2014-08-10T12:20:58Z

Hi Brian,

On Wed, Aug 6, 2014 at 6:20 PM, Brian Foster <bfoster@redhat.com> wrote:
> On Wed, Aug 06, 2014 at 03:52:03PM +0300, Alex Lyakas wrote:
>> Hello Dave and Brian,
>>
>> Dave, I tried the patch you suggested, but it does not fix the issue. I did
>> some further digging, and it appears that _xfs_buf_ioend(schedule=1) can be
>> called from xfs_buf_iorequest(), which the patch fixes, but also from
>> xfs_buf_bio_end_io() which is my case. I am reproducing the issue pretty
>> easily. The flow that I have is like this:
>> - xlog_recover() calls xlog_find_tail(). This works alright.
>
> What's the purpose of a sleep here?
>
>> - Now I add a small sleep before calling xlog_do_recover(), and meanwhile I
>> instruct my block device to return ENOSPC for any WRITE from now on.
>>
>> What seems to happen is that several WRITE bios are submitted and they all
>> fail. When they do, they reach xfs_buf_ioend() through a stack like this:
>>
>> Aug 6 15:23:07 dev kernel: [ 304.410528] [56]xfs*[xfs_buf_ioend:1056]
>> XFS(dm-19): Scheduling xfs_buf_iodone_work on error
>> Aug 6 15:23:07 dev kernel: [ 304.410534] Pid: 56, comm: kworker/u:1
>> Tainted: G W O 3.8.13-557-generic #1382000791
>> Aug 6 15:23:07 dev kernel: [ 304.410537] Call Trace:
>> Aug 6 15:23:07 dev kernel: [ 304.410587] [<ffffffffa04d6654>]
>> xfs_buf_ioend+0x1a4/0x1b0 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.410621] [<ffffffffa04d6685>]
>> _xfs_buf_ioend+0x25/0x30 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.410643] [<ffffffffa04d6b3d>]
>> xfs_buf_bio_end_io+0x3d/0x50 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.410652] [<ffffffff811c3d8d>]
>> bio_endio+0x1d/0x40
>> ...
>>
>> At this point, they are scheduled to run xlog_recover_iodone through
>> xfslogd_workqueue.
>> The first callback that gets called, calls xfs_do_force_shutdown in stack
>> like this:
>>
>> Aug 6 15:23:07 dev kernel: [ 304.411791] XFS (dm-19): metadata I/O error:
>> block 0x3780001 ("xlog_recover_iodone") error 28 numblks 1
>> Aug 6 15:23:07 dev kernel: [ 304.413493] XFS (dm-19):
>> xfs_do_force_shutdown(0x1) called from line 377 of file
>> /mnt/work/alex/xfs/fs/xfs/xfs_log_recover.c. Return address =
>> 0xffffffffa0526848
>> Aug 6 15:23:07 dev kernel: [ 304.413837] [<ffffffffa04e0b60>]
>> xfs_do_force_shutdown+0x40/0x180 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.413870] [<ffffffffa0526848>] ?
>> xlog_recover_iodone+0x48/0x70 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.413902] [<ffffffffa0526848>]
>> xlog_recover_iodone+0x48/0x70 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.413923] [<ffffffffa04d645d>]
>> xfs_buf_iodone_work+0x4d/0xa0 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.413930] [<ffffffff81077a11>]
>> process_one_work+0x141/0x4a0
>> Aug 6 15:23:07 dev kernel: [ 304.413937] [<ffffffff810789e8>]
>> worker_thread+0x168/0x410
>> Aug 6 15:23:07 dev kernel: [ 304.413943] [<ffffffff81078880>] ?
>> manage_workers+0x120/0x120
>> Aug 6 15:23:07 dev kernel: [ 304.413949] [<ffffffff8107df10>]
>> kthread+0xc0/0xd0
>> Aug 6 15:23:07 dev kernel: [ 304.413954] [<ffffffff8107de50>] ?
>> flush_kthread_worker+0xb0/0xb0
>> Aug 6 15:23:07 dev kernel: [ 304.413976] [<ffffffff816ab86c>]
>> ret_from_fork+0x7c/0xb0
>> Aug 6 15:23:07 dev kernel: [ 304.413986] [<ffffffff8107de50>] ?
>> flush_kthread_worker+0xb0/0xb0
>> Aug 6 15:23:07 dev kernel: [ 304.413990] ---[ end trace 988d698520e1fa81
>> ]---
>> Aug 6 15:23:07 dev kernel: [ 304.414012] XFS (dm-19): I/O Error Detected.
>> Shutting down filesystem
>> Aug 6 15:23:07 dev kernel: [ 304.415936] XFS (dm-19): Please umount the
>> filesystem and rectify the problem(s)
>>
>> But the rest of the callbacks also arrive:
>> Aug 6 15:23:07 dev kernel: [ 304.417812] XFS (dm-19): metadata I/O error:
>> block 0x3780002 ("xlog_recover_iodone") error 28 numblks 1
>> Aug 6 15:23:07 dev kernel: [ 304.420420] XFS (dm-19):
>> xfs_do_force_shutdown(0x1) called from line 377 of file
>> /mnt/work/alex/xfs/fs/xfs/xfs_log_recover.c. Return address =
>> 0xffffffffa0526848
>> Aug 6 15:23:07 dev kernel: [ 304.420427] XFS (dm-19): metadata I/O error:
>> block 0x3780008 ("xlog_recover_iodone") error 28 numblks 8
>> Aug 6 15:23:07 dev kernel: [ 304.422708] XFS (dm-19):
>> xfs_do_force_shutdown(0x1) called from line 377 of file
>> /mnt/work/alex/xfs/fs/xfs/xfs_log_recover.c. Return address =
>> 0xffffffffa0526848
>> Aug 6 15:23:07 dev kernel: [ 304.422738] XFS (dm-19): metadata I/O error:
>> block 0x3780010 ("xlog_recover_iodone") error 28 numblks 8
>>
>> The mount sequence fails and goes back to the caller:
>> Aug 6 15:23:07 dev kernel: [ 304.423438] XFS (dm-19): log mount/recovery
>> failed: error 28
>> Aug 6 15:23:07 dev kernel: [ 304.423757] XFS (dm-19): log mount failed
>>
>> But there are still additional callbacks to deliver, which the mount
>> sequence did not wait for!
>> Aug 6 15:23:07 dev kernel: [ 304.425717] XFS ( @dR):
>> xfs_do_force_shutdown(0x1) called from line 377 of file
>> /mnt/work/alex/xfs/fs/xfs/xfs_log_recover.c. Return address =
>> 0xffffffffa0526848
>> Aug 6 15:23:07 dev kernel: [ 304.425723] XFS ( @dR): metadata I/O error:
>> block 0x3780018 ("xlog_recover_iodone") error 28 numblks 8
>> Aug 6 15:23:07 dev kernel: [ 304.428239] XFS ( @dR):
>> xfs_do_force_shutdown(0x1) called from line 377 of file
>> /mnt/work/alex/xfs/fs/xfs/xfs_log_recover.c. Return address =
>> 0xffffffffa0526848
>> Aug 6 15:23:07 dev kernel: [ 304.428246] XFS ( @dR): metadata I/O error:
>> block 0x37800a0 ("xlog_recover_iodone") error 28 numblks 16
>>
>> Notice the junk that they are printing! Naturally, because xfs_mount
>> structure has been kfreed.
>>
>> Finally the kernel crashes (instead of printing junk), because the xfs_mount
>> structure is gone, but the callback tries to access it (printing the name):
>>
>> Aug 6 15:23:07 dev kernel: [ 304.430796] general protection fault: 0000
>> [#1] SMP
>> Aug 6 15:23:07 dev kernel: [ 304.432035] Modules linked in: xfrm_user
>> xfrm4_tunnel tunnel4 ipcomp xfrm_ipcomp esp4 ah4 iscsi_scst_tcp(O)
>> scst_vdisk(O) scst(O) dm_zcache(O) dm_btrfs(O) xfs(O) btrfs(O) libcrc32c
>> raid456(O) async_pq async_xor xor async_memcpy async_raid6_recov raid6_pq
>> async_tx raid1(O) md_mod deflate zlib_deflate ctr twofish_generic
>> twofish_x86_64_3way glue_helper lrw xts gf128mul twofish_x86_64
>> twofish_common camellia_generic serpent_generic blowfish_generic
>> blowfish_x86_64 blowfish_common cast5_generic cast_common des_generic xcbc
>> rmd160 sha512_generic crypto_null af_key xfrm_algo dm_round_robin kvm vfat
>> fat ppdev psmouse microcode nfsd nfs_acl dm_multipath(O) serio_raw
>> parport_pc nfsv4 dm_iostat(O) mac_hid i2c_piix4 auth_rpcgss nfs fscache
>> lockd sunrpc lp parport floppy
>> Aug 6 15:23:07 dev kernel: [ 304.432035] CPU 1
>> Aug 6 15:23:07 dev kernel: [ 304.432035] Pid: 133, comm: kworker/1:1H
>> Tainted: G W O 3.8.13-557-generic #1382000791 Bochs Bochs
>> Aug 6 15:23:07 dev kernel: [ 304.432035] RIP: 0010:[<ffffffff8133c2cb>]
>> [<ffffffff8133c2cb>] strnlen+0xb/0x30
>> Aug 6 15:23:07 dev kernel: [ 304.432035] RSP: 0018:ffff880035461b08
>> EFLAGS: 00010086
>> Aug 6 15:23:07 dev kernel: [ 304.432035] RAX: 0000000000000000 RBX:
>> ffffffff81e6a4e7 RCX: 0000000000000000
>> Aug 6 15:23:07 dev kernel: [ 304.432035] RDX: e4e8390a265c0000 RSI:
>> ffffffffffffffff RDI: e4e8390a265c0000
>> Aug 6 15:23:07 dev kernel: [ 304.432035] RBP: ffff880035461b08 R08:
>> 000000000000ffff R09: 000000000000ffff
>> Aug 6 15:23:07 dev kernel: [ 304.432035] R10: 0000000000000000 R11:
>> 00000000000004cd R12: e4e8390a265c0000
>> Aug 6 15:23:07 dev kernel: [ 304.432035] R13: ffffffff81e6a8c0 R14:
>> 0000000000000000 R15: 000000000000ffff
>> Aug 6 15:23:07 dev kernel: [ 304.432035] FS: 0000000000000000(0000)
>> GS:ffff88007fc80000(0000) knlGS:0000000000000000
>> Aug 6 15:23:07 dev kernel: [ 304.432035] CS: 0010 DS: 0000 ES: 0000 CR0:
>> 000000008005003b
>> Aug 6 15:23:07 dev kernel: [ 304.432035] CR2: 00007fc902ffbfd8 CR3:
>> 000000007702a000 CR4: 00000000000006e0
>> Aug 6 15:23:07 dev kernel: [ 304.432035] DR0: 0000000000000000 DR1:
>> 0000000000000000 DR2: 0000000000000000
>> Aug 6 15:23:07 dev kernel: [ 304.432035] DR3: 0000000000000000 DR6:
>> 00000000ffff0ff0 DR7: 0000000000000400
>> Aug 6 15:23:07 dev kernel: [ 304.432035] Process kworker/1:1H (pid: 133,
>> threadinfo ffff880035460000, task ffff880035412e00)
>> Aug 6 15:23:07 dev kernel: [ 304.432035] Stack:
>> Aug 6 15:23:07 dev kernel: [ 304.432035] ffff880035461b48
>> ffffffff8133dd5e 0000000000000000 ffffffff81e6a4e7
>> Aug 6 15:23:07 dev kernel: [ 304.432035] ffffffffa0566cba
>> ffff880035461c80 ffffffffa0566cba ffffffff81e6a8c0
>> Aug 6 15:23:07 dev kernel: [ 304.432035] ffff880035461bc8
>> ffffffff8133ef59 ffff880035461bc8 ffffffff81c84040
>> Aug 6 15:23:07 dev kernel: [ 304.432035] Call Trace:
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8133dd5e>]
>> string.isra.4+0x3e/0xd0
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8133ef59>]
>> vsnprintf+0x219/0x640
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8133f441>]
>> vscnprintf+0x11/0x30
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8105a971>]
>> vprintk_emit+0xc1/0x490
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8105aa20>] ?
>> vprintk_emit+0x170/0x490
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8168b992>]
>> printk+0x61/0x63
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffffa04e9bf1>]
>> __xfs_printk+0x31/0x50 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffffa04e9e43>]
>> xfs_notice+0x53/0x60 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffffa04e0c15>]
>> xfs_do_force_shutdown+0xf5/0x180 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffffa0526848>] ?
>> xlog_recover_iodone+0x48/0x70 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffffa0526848>]
>> xlog_recover_iodone+0x48/0x70 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffffa04d645d>]
>> xfs_buf_iodone_work+0x4d/0xa0 [xfs]
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff81077a11>]
>> process_one_work+0x141/0x4a0
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff810789e8>]
>> worker_thread+0x168/0x410
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff81078880>] ?
>> manage_workers+0x120/0x120
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8107df10>]
>> kthread+0xc0/0xd0
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8107de50>] ?
>> flush_kthread_worker+0xb0/0xb0
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff816ab86c>]
>> ret_from_fork+0x7c/0xb0
>> Aug 6 15:23:07 dev kernel: [ 304.432035] [<ffffffff8107de50>] ?
>> flush_kthread_worker+0xb0/0xb0
>> Aug 6 15:23:07 dev kernel: [ 304.432035] Code: 31 c0 80 3f 00 55 48 89 e5
>> 74 11 48 89 f8 66 90 48 83 c0 01 80 38 00 75 f7 48 29 f8 5d c3 66 90 55 31
>> c0 48 85 f6 48 89 e5 74 23 <80> 3f 00 74 1e 48 89 f8 eb 0c 0f 1f 00 48 83 ee
>> 01 80 38 00 74
>> Aug 6 15:23:07 dev kernel: [ 304.432035] RIP [<ffffffff8133c2cb>]
>> strnlen+0xb/0x30
>> Aug 6 15:23:07 dev kernel: [ 304.432035] RSP <ffff880035461b08>
>>
>>
>> So previously you said: "So, something is corrupting memory and stamping all
>> over the XFS structures." and also "given you have a bunch of out of tree
>> modules loaded (and some which are experiemental) suggests that you have a
>> problem with your storage...".
>>
>> But I believe, my analysis shows that during the mount sequence XFS does not
>> wait properly for all the bios to complete, before failing the mount
>> sequence back to the caller.
>>
>
> As an experiment, what about the following? Compile tested only and not
> safe for general use.
>
> What might help more is to see if you can create a reproducer on a
> recent, clean kernel. Perhaps a metadump of your reproducer fs combined
> with whatever block device ENOSPC hack you're using would do it.
>
> Brian
>
> ---8<---
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index cd7b8ca..fbcf524 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1409,19 +1409,27 @@ xfs_buf_iorequest(
> * case nothing will ever complete. It returns the I/O error code, if any, or
> * 0 if there was no error.
> */
> -int
> -xfs_buf_iowait(
> - xfs_buf_t *bp)
> +static int
> +__xfs_buf_iowait(
> + struct xfs_buf *bp,
> + bool skip_error)
> {
> trace_xfs_buf_iowait(bp, _RET_IP_);
>
> - if (!bp->b_error)
> + if (skip_error || !bp->b_error)
> wait_for_completion(&bp->b_iowait);
>
> trace_xfs_buf_iowait_done(bp, _RET_IP_);
> return bp->b_error;
> }
>
> +int
> +xfs_buf_iowait(
> + struct xfs_buf *bp)
> +{
> + return __xfs_buf_iowait(bp, false);
> +}
> +
> xfs_caddr_t
> xfs_buf_offset(
> xfs_buf_t *bp,
> @@ -1866,7 +1874,7 @@ xfs_buf_delwri_submit(
> bp = list_first_entry(&io_list, struct xfs_buf, b_list);
>
> list_del_init(&bp->b_list);
> - error2 = xfs_buf_iowait(bp);
> + error2 = __xfs_buf_iowait(bp, true);
> xfs_buf_relse(bp);
> if (!error)
> error = error2;
>
> ---
I think that this patch fixes the problem. I tried reproducing it like
30 times, and it doesn't happen with this patch. Dropping this patch
reproduces the problem within 1 or 2 tries. Thanks!
What are next steps? How to make it "safe for general use"?

Thanks,
Alex.

>
>> Thanks,
>> Alex.
>>
>>
>>
>> -----Original Message----- From: Dave Chinner
>> Sent: 05 August, 2014 2:07 AM
>> To: Alex Lyakas
>> Cc: xfs@oss.sgi.com
>> Subject: Re: use-after-free on log replay failure
>>
>> On Mon, Aug 04, 2014 at 02:00:05PM +0300, Alex Lyakas wrote:
>> >Greetings,
>> >
>> >we had a log replay failure due to some errors that the underlying
>> >block device returned:
>> >[49133.801406] XFS (dm-95): metadata I/O error: block 0x270e8c180
>> >("xlog_recover_iodone") error 28 numblks 16
>> >[49133.802495] XFS (dm-95): log mount/recovery failed: error 28
>> >[49133.802644] XFS (dm-95): log mount failed
>>
>> #define ENOSPC 28 /* No space left on device */
>>
>> You're getting an ENOSPC as a metadata IO error during log recovery?
>> Thin provisioning problem, perhaps, and the error is occurring on
>> submission rather than completion? If so:
>>
>> 8d6c121 xfs: fix buffer use after free on IO error
>>
>> Cheers,
>>
>> Dave.
>> --
>> Dave Chinner
>> david@fromorbit.com
>>