Re: kernel BUG at kernel/fork.c:LINE!

[Randy Dunlap]

On 8/7/20 2:16 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    fffe3ae0 Merge tag 'for-linus-hmm' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1194d90a900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=18bb86f2e4ebfda2
> dashboard link: https://syzkaller.appspot.com/bug?extid=3776ecd80aac504e6085
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3776ecd80aac504e6085@xxxxxxxxxxxxxxxxxxxxxxxxx

Is this fixed by

commit 991e7673859ed41e7ba83c8c4e57afe8cfebe314
Author: Shakeel Butt <shakeelb@xxxxxxxxxx>
Date:   Thu Aug 6 23:21:37 2020 -0700

    mm: memcontrol: account kernel stack per node


since the BUG_ON() at line 390 is removed by this patch.


> ------------[ cut here ]------------
> kernel BUG at kernel/fork.c:390!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 5239 Comm: syz-executor.1 Not tainted 5.8.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:account_kernel_stack+0x297/0x320 kernel/fork.c:390
> Code: 89 e2 be 23 00 00 00 48 89 ef c1 e2 05 e8 81 9e 75 00 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f e9 ae c9 2f 00 e8 a9 c9 2f 00 <0f> 0b e8 f2 50 6f 00 e9 d2 fd ff ff e8 98 c9 2f 00 48 c7 c6 20 24
> RSP: 0018:ffffc90015e4f850 EFLAGS: 00010216
> RAX: 00000000000001f4 RBX: 0000000000000000 RCX: ffffc90017983000
> RDX: 0000000000040000 RSI: ffffffff81445327 RDI: 0000000000000005
> RBP: 0000000000000000 R08: 0000000000000001 R09: ffff8880a2ef9663
> R10: 0000000000000008 R11: 0000000000000000 R12: ffffffffffffffff
> R13: ffff8880001b2280 R14: ffff88809e4fa840 R15: 0000000000000000
> FS:  00007f7f035e5700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b2fd30000 CR3: 000000009b747000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  release_task_stack kernel/fork.c:447 [inline]
>  put_task_stack+0xc4/0x230 kernel/fork.c:459
>  finish_task_switch+0x52a/0x750 kernel/sched/core.c:3649
>  context_switch kernel/sched/core.c:3781 [inline]
>  __schedule+0x8ed/0x21e0 kernel/sched/core.c:4527
>  schedule+0xd0/0x2a0 kernel/sched/core.c:4602
>  freezable_schedule include/linux/freezer.h:172 [inline]
>  futex_wait_queue_me+0x2a7/0x570 kernel/futex.c:2588
>  futex_wait+0x1df/0x560 kernel/futex.c:2690
>  do_futex+0x15b/0x1a60 kernel/futex.c:3749
>  __do_sys_futex kernel/futex.c:3810 [inline]
>  __se_sys_futex kernel/futex.c:3778 [inline]
>  __x64_sys_futex+0x378/0x4e0 kernel/futex.c:3778
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x45ccd9
> Code: 2d 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 fb b5 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f7f035e4cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
> RAX: ffffffffffffffda RBX: 000000000078bfa8 RCX: 000000000045ccd9
> RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000078bfa8
> RBP: 000000000078bfa0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078bfac
> R13: 00007fff896cb67f R14: 00007f7f035e59c0 R15: 000000000078bfac
> Modules linked in:
> ---[ end trace ff14b6c5822b8142 ]---
> RIP: 0010:account_kernel_stack+0x297/0x320 kernel/fork.c:390
> Code: 89 e2 be 23 00 00 00 48 89 ef c1 e2 05 e8 81 9e 75 00 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f e9 ae c9 2f 00 e8 a9 c9 2f 00 <0f> 0b e8 f2 50 6f 00 e9 d2 fd ff ff e8 98 c9 2f 00 48 c7 c6 20 24
> RSP: 0018:ffffc90015e4f850 EFLAGS: 00010216
> RAX: 00000000000001f4 RBX: 0000000000000000 RCX: ffffc90017983000
> RDX: 0000000000040000 RSI: ffffffff81445327 RDI: 0000000000000005
> RBP: 0000000000000000 R08: 0000000000000001 R09: ffff8880a2ef9663
> R10: 0000000000000008 R11: 0000000000000000 R12: ffffffffffffffff
> R13: ffff8880001b2280 R14: ffff88809e4fa840 R15: 0000000000000000
> FS:  00007f7f035e5700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b2fd30000 CR3: 000000009b747000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> ---
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-- 
~Randy