Re: kernel BUG at fs/ext4/fsync.c:LINE!

[Andreas Dilger]

On Sep 14, 2017, at 9:04 AM, ChunYu Wang <chunwang@xxxxxxxxxx> wrote:
> 
> Hi GeneBlue,
> 
> Thanks for this reporting, do you have any logs related to the bug and
> could find the syscalls enabled for fuzzing during triggering this
> bug? I do not think it is not reproducible, but first, it needs some
> inspections manually.

I don't think a reproducer is needed.  It looks like the fsync callpath
is happening from an IRQ context due to IO completion, and then re-entering
the filesystem while a transaction is already started.  It looks like the
original IO was submitted with AIO based on the functions on the IRQ stack,
which is likely why nobody has hit it (AIO isn't very commonly used).

That said, I don't follow the reasoning behind the convoluted series of AIO
callbacks that has IO _completion_ calling vfs_fsync_range() and re-entering
the filesystem to flush out more data?

Cheers, Andreas

> On Thu, Sep 14, 2017 at 7:54 PM, GeneBlue <geneblue.mail@xxxxxxxxx> wrote:
>> Hi:
>>  I've got this crash when fuzzing linux kernel 4.13.0-rc7 on commit
>> 42ff72cf27027fa28dd79acabe01d9196f1480a7. Unfortunately this crash is not
>> reproducible. And this crash was found by syzkaller.
>> 
>> 
>> ------------[ cut here ]------------
>> kernel BUG at fs/ext4/fsync.c:106!
>> invalid opcode: 0000 [#1] SMP KASAN
>> Dumping ftrace buffer:
>>   (ftrace buffer empty)
>> Modules linked in:
>> CPU: 0 PID: 25424 Comm: syz-executor5 Not tainted 4.13.0-rc7+ #2
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
>> task: ffff880038690000 task.stack: ffff880024648000
>> RIP: 0010:ext4_sync_file+0x7b6/0xfb0 fs/ext4/fsync.c:106
>> RSP: 0018:ffff88003ec07ae0 EFLAGS: 00010206
>> RAX: ffff880038690000 RBX: ffff8800239adaa0 RCX: dffffc0000000000
>> RDX: 0000000000000100 RSI: 1ffff100070d21ff RDI: ffff880038690ff8
>> RBP: ffff88003ec07b30 R08: dffffc0000000000 R09: 1ffff1000cbf5730
>> R10: dffffc0000000000 R11: 1ffff1000cbf58f7 R12: ffff880065fab300
>> R13: ffff88003dc36a80 R14: ffff880065fac400 R15: ffff880038690000
>> FS:  0000000002188940(0000) GS:ffff88003ec00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007ffd1350fbb0 CR3: 000000002718d000 CR4: 00000000000006f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
>> Call Trace:
>> <IRQ>
>> vfs_fsync_range+0x10c/0x250 fs/sync.c:195
>> generic_write_sync include/linux/fs.h:2625 [inline]
>> dio_complete+0x564/0x710 fs/direct-io.c:282
>> dio_bio_end_aio+0x120/0x360 fs/direct-io.c:323
>> bio_endio+0x1df/0x5d0 block/bio.c:1839
>> req_bio_endio block/blk-core.c:204 [inline]
>> blk_update_request+0x210/0xd30 block/blk-core.c:2729
>> scsi_end_request+0xa7/0x5b0 drivers/scsi/scsi_lib.c:634
>> scsi_io_completion+0x73d/0x1430 drivers/scsi/scsi_lib.c:834
>> scsi_finish_command+0x3e9/0x560 drivers/scsi/scsi.c:248
>> scsi_softirq_done+0x2db/0x360 drivers/scsi/scsi_lib.c:1602
>> blk_done_softirq+0x247/0x380 block/blk-softirq.c:36
>> __do_softirq+0x23f/0x924 kernel/softirq.c:284
>> invoke_softirq kernel/softirq.c:364 [inline]
>> irq_exit+0x1a7/0x1e0 kernel/softirq.c:405
>> exiting_irq arch/x86/include/asm/apic.h:638 [inline]
>> do_IRQ+0x81/0x1a0 arch/x86/kernel/irq.c:256
>> common_interrupt+0x93/0x93 arch/x86/entry/entry_64.S:482
>> RIP: 0010:__ext4_handle_dirty_metadata+0x5d/0x5c0 fs/ext4/ext4_jbd2.c:275
>> RSP: 0018:ffff88002464f9d0 EFLAGS: 00000297 ORIG_RAX: ffffffffffffffc1
>> RAX: ffff880038690000 RBX: ffff88003e4199d8 RCX: 0000000000000000
>> RDX: 0000000000000000 RSI: ffff88003e4199d8 RDI: ffff88003869004c
>> RBP: ffff88002464fa18 R08: 0000000000000007 R09: dffffc0000000000
>> R10: 1ffff100070d211c R11: 0000000000000000 R12: ffff8800381f95c0
>> R13: 0000000000000000 R14: 00000000000000a0 R15: 000000000000141f
>> </IRQ>
>> ext4_do_update_inode fs/ext4/inode.c:5151 [inline]
>> ext4_mark_iloc_dirty+0x17e1/0x2980 fs/ext4/inode.c:5673
>> ext4_orphan_del+0x711/0x930 fs/ext4/namei.c:2901
>> ext4_evict_inode+0xe6b/0x1690 fs/ext4/inode.c:308
>> evict+0x248/0x620 fs/inode.c:553
>> iput_final fs/inode.c:1514 [inline]
>> iput+0x538/0x840 fs/inode.c:1541
>> do_unlinkat+0x28b/0x640 fs/namei.c:4049
>> SYSC_unlink fs/namei.c:4090 [inline]
>> SyS_unlink+0x1a/0x20 fs/namei.c:4088
>> entry_SYSCALL_64_fastpath+0x1f/0xbe
>> RIP: 0033:0x447077
>> RSP: 002b:00007ffd135102e8 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
>> RAX: ffffffffffffffda RBX: 0000000000000066 RCX: 0000000000447077
>> RDX: 00007ffd13510300 RSI: 00007ffd13510390 RDI: 00007ffd13510390
>> RBP: 0000000000000046 R08: 0000000000000000 R09: 000000000218acdb
>> R10: 0000000000000005 R11: 0000000000000206 R12: 00000000004a8919
>> R13: 00007ffd13510218 R14: 0000000000000001 R15: 00007ffd13510218
>> Code: 8b 4d c0 41 f6 01 20 0f 85 1c 03 00 00 e8 f3 ae bb ff 48 8b 7d c0 44
>> 89 e6 e8 37 76 13 00 41 89 c4 e9 dc fa ff ff e8 da ae bb ff <0f> 0b e8 d3 ae
>> bb ff 8b 4d d4 48 8b 55 b0 4c 89 ef 48 8b 75 b8
>> RIP: ext4_sync_file+0x7b6/0xfb0 fs/ext4/fsync.c:106 RSP: ffff88003ec07ae0
>> ---[ end trace 3049124842185959 ]---
>> 
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Cheers, Andreas

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