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Date:   Mon, 13 Apr 2020 13:32:16 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     syzbot <syzbot+2854d22c7dd957a6519a@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com, Evan Green <evgreen@...omium.org>,
        Martijn Coenen <maco@...roid.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: WARNING in unaccount_page_cache_page (2)

On Mon, 13 Apr 2020 00:50:11 -0700 syzbot <syzbot+2854d22c7dd957a6519a@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    ae46d2aa mm/gup: Let __get_user_pages_locked() return -EIN..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12b60343e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ca75979eeebf06c2
> dashboard link: https://syzkaller.appspot.com/bug?extid=2854d22c7dd957a6519a
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+2854d22c7dd957a6519a@...kaller.appspotmail.com

(cc's added)

Looks like the loop backing device's pagecache still has a dirty page,
despite us having just run sync_blockdev().  It may well be a race of
some form - do we have any description of what the test is doing?


> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 8402 at mm/filemap.c:222 unaccount_page_cache_page+0x631/0xd60 mm/filemap.c:222
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 8402 Comm: syz-executor.4 Not tainted 5.6.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x188/0x20d lib/dump_stack.c:118
>  panic+0x2e3/0x75c kernel/panic.c:221
>  __warn.cold+0x2f/0x35 kernel/panic.c:582
>  report_bug+0x27b/0x2f0 lib/bug.c:195
>  fixup_bug arch/x86/kernel/traps.c:175 [inline]
>  fixup_bug arch/x86/kernel/traps.c:170 [inline]
>  do_error_trap+0x12b/0x220 arch/x86/kernel/traps.c:267
>  do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
>  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
> RIP: 0010:unaccount_page_cache_page+0x631/0xd60 mm/filemap.c:222
> Code: 02 00 0f 85 3a 06 00 00 48 8b 1b 31 ff 48 c1 eb 03 83 e3 01 48 89 de e8 9d 01 e2 ff 48 85 db 0f 84 d9 fb ff ff e8 ff ff e1 ff <0f> 0b 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 80 3c 02
> RSP: 0018:ffffc90001287688 EFLAGS: 00010012
> RAX: 0000000000040000 RBX: 0000000000000001 RCX: ffffc90011a34000
> RDX: 000000000000ec1b RSI: ffffffff81913191 RDI: 0000000000000007
> RBP: ffffea0001165dc0 R08: ffff88804a3ce240 R09: fffff9400022cbb9
> R10: ffffea0001165dc7 R11: fffff9400022cbb8 R12: 0000000000000000
> R13: ffff8880a3f6bbe0 R14: ffffea0001165dc0 R15: ffffea00022cd088
>  delete_from_page_cache_batch+0x1a6/0xec0 mm/filemap.c:355
>  truncate_inode_pages_range+0x58b/0x1760 mm/truncate.c:366
>  kill_bdev+0xd1/0x100 fs/block_dev.c:87
>  loop_set_status+0x315/0x1370 drivers/block/loop.c:1272
>  loop_set_status_old+0x223/0x310 drivers/block/loop.c:1468
>  lo_ioctl+0x308/0x1410 drivers/block/loop.c:1612
>  __blkdev_driver_ioctl block/ioctl.c:322 [inline]
>  blkdev_ioctl+0x25b/0x660 block/ioctl.c:718
>  block_ioctl+0xf9/0x140 fs/block_dev.c:1996
>  vfs_ioctl fs/ioctl.c:47 [inline]
>  ksys_ioctl+0x11a/0x180 fs/ioctl.c:763
>  __do_sys_ioctl fs/ioctl.c:772 [inline]
>  __se_sys_ioctl fs/ioctl.c:770 [inline]
>  __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:770
>  do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
>  entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x45c889
> Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f83d100ac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f83d100b6d4 RCX: 000000000045c889
> RDX: 0000000020000440 RSI: 0000000000004c02 RDI: 0000000000000003
> RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000000003f4 R14: 00000000004c6902 R15: 000000000076bf0c
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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