Re: [syzbot] [bcachefs?] BUG: unable to handle kernel paging request in pipe_write

[Kent Overstreet]

So this is after a bcachefs failure to mount - filesystem bringup error
path - which implies we've got a memory stomper that kasan isn't able to
catch.

There's a couple that fit that pattern, and I think percpu allocations
were involved in all of them...

On Thu, Mar 06, 2025 at 11:50:20PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    848e07631744 Merge tag 'hid-for-linus-2025030501' of git:/..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=173c4a64580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2040405600e83619
> dashboard link: https://syzkaller.appspot.com/bug?extid=46cddce16efb51810fff
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10c7fda8580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-848e0763.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/c46426c0526b/vmlinux-848e0763.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/d575feb1a7df/bzImage-848e0763.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/50b3934b613c/mount_0.gz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+46cddce16efb51810fff@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> BUG: unable to handle page fault for address: ffff887fabfbcf80
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD 0 P4D 0 
> Oops: Oops: 0002 [#1] PREEMPT SMP KASAN NOPTI
> CPU: 0 UID: 0 PID: 5336 Comm: syz-executor Not tainted 6.14.0-rc5-syzkaller-00039-g848e07631744 #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:__percpu_down_read_trylock kernel/locking/percpu-rwsem.c:50 [inline]
> RIP: 0010:__percpu_down_read+0x40/0x130 kernel/locking/percpu-rwsem.c:169
> Code: 49 bd 00 00 00 00 00 fc ff df 4c 8d 77 68 4c 89 f5 48 c1 ed 03 42 80 7c 2d 00 00 74 08 4c 89 f7 e8 35 7e 1e f6 49 8b 44 24 68 <65> ff 00 f0 83 44 24 fc 00 49 8d 9c 24 c8 00 00 00 48 89 df be 04
> RSP: 0018:ffffc9000d1c7aa0 EFLAGS: 00010246
> RAX: ffffffff8c3bcf80 RBX: 000000008e29c24b RCX: ffff8880001fc880
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff8ecc2fd8
> RBP: 1ffffffff1d98608 R08: ffffffff823d3401 R09: 1ffffffff2079e8e
> R10: dffffc0000000000 R11: fffffbfff2079e8f R12: ffffffff8ecc2fd8
> R13: dffffc0000000000 R14: ffffffff8ecc3040 R15: ffffffff8ecc2fd8
> FS:  0000555594365500(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff887fabfbcf80 CR3: 000000004349a000 CR4: 0000000000352ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  percpu_down_read_trylock include/linux/percpu-rwsem.h:84 [inline]
>  __sb_start_write_trylock include/linux/fs.h:1790 [inline]
>  sb_start_write_trylock include/linux/fs.h:1926 [inline]
>  pipe_write+0x16db/0x1950 fs/pipe.c:605
>  new_sync_write fs/read_write.c:586 [inline]
>  vfs_write+0xacf/0xd10 fs/read_write.c:679
>  ksys_write+0x18f/0x2b0 fs/read_write.c:731
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fc094d8bbe0
> Code: 40 00 48 c7 c2 a8 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d 61 19 1f 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89
> RSP: 002b:00007ffe88624b48 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 0000555594379d50 RCX: 00007fc094d8bbe0
> RDX: 0000000000000030 RSI: 00007ffe88624b80 RDI: 000000000000000b
> RBP: 0000555594378f20 R08: 0000000005a61143 R09: 7fffffffffffffff
> R10: 00007fc095b50038 R11: 0000000000000202 R12: 0000000000000001
> R13: 0000000000000000 R14: 00007ffe88624b60 R15: 0000000000000000
>  </TASK>
> Modules linked in:
> CR2: ffff887fabfbcf80
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:__percpu_down_read_trylock kernel/locking/percpu-rwsem.c:50 [inline]
> RIP: 0010:__percpu_down_read+0x40/0x130 kernel/locking/percpu-rwsem.c:169
> Code: 49 bd 00 00 00 00 00 fc ff df 4c 8d 77 68 4c 89 f5 48 c1 ed 03 42 80 7c 2d 00 00 74 08 4c 89 f7 e8 35 7e 1e f6 49 8b 44 24 68 <65> ff 00 f0 83 44 24 fc 00 49 8d 9c 24 c8 00 00 00 48 89 df be 04
> RSP: 0018:ffffc9000d1c7aa0 EFLAGS: 00010246
> RAX: ffffffff8c3bcf80 RBX: 000000008e29c24b RCX: ffff8880001fc880
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff8ecc2fd8
> RBP: 1ffffffff1d98608 R08: ffffffff823d3401 R09: 1ffffffff2079e8e
> R10: dffffc0000000000 R11: fffffbfff2079e8f R12: ffffffff8ecc2fd8
> R13: dffffc0000000000 R14: ffffffff8ecc3040 R15: ffffffff8ecc2fd8
> FS:  0000555594365500(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff887fabfbcf80 CR3: 000000004349a000 CR4: 0000000000352ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:	49 bd 00 00 00 00 00 	movabs $0xdffffc0000000000,%r13
>    7:	fc ff df
>    a:	4c 8d 77 68          	lea    0x68(%rdi),%r14
>    e:	4c 89 f5             	mov    %r14,%rbp
>   11:	48 c1 ed 03          	shr    $0x3,%rbp
>   15:	42 80 7c 2d 00 00    	cmpb   $0x0,0x0(%rbp,%r13,1)
>   1b:	74 08                	je     0x25
>   1d:	4c 89 f7             	mov    %r14,%rdi
>   20:	e8 35 7e 1e f6       	call   0xf61e7e5a
>   25:	49 8b 44 24 68       	mov    0x68(%r12),%rax
> * 2a:	65 ff 00             	incl   %gs:(%rax) <-- trapping instruction
>   2d:	f0 83 44 24 fc 00    	lock addl $0x0,-0x4(%rsp)
>   33:	49 8d 9c 24 c8 00 00 	lea    0xc8(%r12),%rbx
>   3a:	00
>   3b:	48 89 df             	mov    %rbx,%rdi
>   3e:	be                   	.byte 0xbe
>   3f:	04                   	.byte 0x4
> 
> 
> ---
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