Date:   Wed, 2 Jan 2019 08:42:23 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     syzbot <syzbot+a5fea9200aefd1cf4818@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, aneesh.kumar@...ux.vnet.ibm.com,
        hughd@...gle.com, jglisse@...hat.com, khlebnikov@...dex-team.ru,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mhocko@...e.com, rientjes@...gle.com,
        sfr@...b.auug.org.au, syzkaller-bugs@...glegroups.com,
        willy@...radead.org
Subject: Re: general protection fault in transparent_hugepage_enabled

On 12/24/18 4:48 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    6a1d293238c1 Add linux-next specific files for 20181224
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=149a2add400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c190b602a5d2d731
> dashboard link: https://syzkaller.appspot.com/bug?extid=a5fea9200aefd1cf4818
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1798bfb7400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17f4dc57400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+a5fea9200aefd1cf4818@...kaller.appspotmail.com
> 
> sshd (6016) used greatest stack depth: 15720 bytes left
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 6032 Comm: syz-executor045 Not tainted 4.20.0-rc7-next-20181224  
> #187
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
> Google 01/01/2011
> RIP: 0010:transparent_hugepage_enabled+0x8c/0x5e0 mm/huge_memory.c:69

FTR, it was most certainly the same thing as here:
https://marc.info/?l=linux-mm&m=154563777207477&w=2

> Code: 80 3c 02 00 0f 85 ae 04 00 00 4c 8b a3 a0 00 00 00 48 b8 00 00 00 00  
> 00 fc ff df 49 8d bc 24 b8 01 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f  
> 85 91 04 00 00 49 8b bc 24 b8 01 00 00 e8 2d 70 e6
> RSP: 0018:ffff8881c2237138 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: ffff8881c2bdbc60 RCX: 0000000000000000
> RDX: 0000000000000037 RSI: ffffffff81c8fa1a RDI: 00000000000001b8
> RBP: ffff8881c2237160 R08: ffffed10383b25ed R09: ffffed10383b25ec
> R10: ffffed10383b25ec R11: ffff8881c1d92f63 R12: 0000000000000000
> R13: ffff8881c2bdbd00 R14: dffffc0000000000 R15: 0000000000000f5e
> FS:  0000000001a48880(0000) GS:ffff8881dad00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020b58000 CR3: 00000001c2210000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   show_smap+0x167/0x580 fs/proc/task_mmu.c:805
>   traverse+0x344/0x7b0 fs/seq_file.c:113
>   seq_read+0xc76/0x1150 fs/seq_file.c:188
>   do_loop_readv_writev fs/read_write.c:700 [inline]
>   do_iter_read+0x4bc/0x670 fs/read_write.c:924
>   vfs_readv+0x175/0x1c0 fs/read_write.c:986
>   kernel_readv fs/splice.c:362 [inline]
>   default_file_splice_read+0x539/0xb20 fs/splice.c:417
>   do_splice_to+0x12e/0x190 fs/splice.c:880
>   splice_direct_to_actor+0x31c/0x9d0 fs/splice.c:957
>   do_splice_direct+0x2d4/0x420 fs/splice.c:1066
>   do_sendfile+0x62a/0xe50 fs/read_write.c:1439
>   __do_sys_sendfile64 fs/read_write.c:1494 [inline]
>   __se_sys_sendfile64 fs/read_write.c:1486 [inline]
>   __x64_sys_sendfile64+0x15d/0x250 fs/read_write.c:1486
>   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x440089
> Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 5b 14 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fff3d710a18 EFLAGS: 00000213 ORIG_RAX: 0000000000000028
> RAX: ffffffffffffffda RBX: 00007fff3d710a20 RCX: 0000000000440089
> RDX: 0000000020b58000 RSI: 0000000000000003 RDI: 0000000000000003
> RBP: 00000000006ca018 R08: 0000000000000010 R09: 65732f636f72702f
> R10: 000000000000ffff R11: 0000000000000213 R12: 0000000000401970
> R13: 0000000000401a00 R14: 0000000000000000 R15: 0000000000000000
> Modules linked in:
> ---[ end trace faf026efd8795e93 ]---
> RIP: 0010:transparent_hugepage_enabled+0x8c/0x5e0 mm/huge_memory.c:69
> Code: 80 3c 02 00 0f 85 ae 04 00 00 4c 8b a3 a0 00 00 00 48 b8 00 00 00 00  
> 00 fc ff df 49 8d bc 24 b8 01 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f  
> 85 91 04 00 00 49 8b bc 24 b8 01 00 00 e8 2d 70 e6
> RSP: 0018:ffff8881c2237138 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: ffff8881c2bdbc60 RCX: 0000000000000000
> RDX: 0000000000000037 RSI: ffffffff81c8fa1a RDI: 00000000000001b8
> RBP: ffff8881c2237160 R08: ffffed10383b25ed R09: ffffed10383b25ec
> R10: ffffed10383b25ec R11: ffff8881c1d92f63 R12: 0000000000000000
> R13: ffff8881c2bdbd00 R14: dffffc0000000000 R15: 0000000000000f5e
> FS:  0000000001a48880(0000) GS:ffff8881dad00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020b58000 CR3: 00000001c2210000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> ---
> 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#bug-status-tracking for how to communicate with  
> syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

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