On Mon, Mar 21, 2022 at 05:29:22AM -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 56e337f2cf13 Revert "gpio: Revert regression in sysfs-gpio.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=146069d9700000 > kernel config: https://syzkaller.appspot.com/x/.config?x=70f75a89c7a0e6bc > dashboard link: https://syzkaller.appspot.com/bug?extid=0d2b0bf32ca5cfd09f2e > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > Unfortunately, I don't have any reproducer for this issue yet. I do! Thanks for the report; I thought deeply about what the problem might be and wrote a test that produces this problem: $ ./xarray linux/../../../../include/linux/xarray.h:1208:9: runtime error: member access within null pointer of type 'const struct xa_node' AddressSanitizer:DEADLYSIGNAL ================================================================= ==2288654==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000008 (pc 0x5636348abdcb bp 0x000000000000 sp 0x7ffd64c7a570 T0) ==2288654==The signal is caused by a READ memory access. ==2288654==Hint: address points to the zero page. #0 0x5636348abdcb in xa_parent_locked linux/../../../../include/linux/xarray.h:1208 #1 0x5636348abdcb in xas_create_range ../../../lib/xarray.c:725 #2 0x5636348b40d1 in check_create_range_5 ../../../lib/test_xarray.c:1474 #3 0x5636348d49da in check_create_range ../../../lib/test_xarray.c:1510 #4 0x5636348d7dc9 in xarray_checks ../../../lib/test_xarray.c:1808 I'll fix it. It's a race condition to reproduce it (khugepaged vs ... actually, I'm not sure what it's racing against, but the other thing also creates a THP before khugepaged gets the lock). There's no way to write a reliable reproducer in userspace, but trivial to write the test-case once you know what's happening. > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+0d2b0bf32ca5cfd09f2e@xxxxxxxxxxxxxxxxxxxxxxxxx > > general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN > KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] > CPU: 0 PID: 32 Comm: khugepaged Not tainted 5.17.0-rc8-syzkaller-00003-g56e337f2cf13 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:xa_parent_locked include/linux/xarray.h:1207 [inline] > RIP: 0010:xas_create_range+0x2d9/0x6e0 lib/xarray.c:725 > Code: 89 ee 49 83 ed 40 49 c1 ee 03 4c 89 6d 08 4c 8d 6d 12 4d 01 e6 e9 93 00 00 00 e8 d2 0f 72 fd 48 8d 7b 08 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 0f 85 fb 02 00 00 48 8b 04 24 4c 8b 7b 08 80 38 00 > RSP: 0018:ffffc90001097a48 EFLAGS: 00010002 > RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000000 > RDX: ffff8880139de240 RSI: ffffffff8405e5be RDI: 0000000000000008 > RBP: ffffc90001097bb0 R08: 0000000000000000 R09: 0000000000000000 > R10: ffffffff8405e679 R11: 0000000000000000 R12: dffffc0000000000 > R13: ffffc90001097bc2 R14: fffff52000212f76 R15: 0000000000000001 > FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007ffe25571c98 CR3: 0000000079206000 CR4: 00000000003506f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > <TASK> > collapse_file+0x2d3/0x3c40 mm/khugepaged.c:1678 > khugepaged_scan_file mm/khugepaged.c:2073 [inline] > khugepaged_scan_mm_slot mm/khugepaged.c:2168 [inline] > khugepaged_do_scan mm/khugepaged.c:2252 [inline] > khugepaged+0x53c7/0x6c00 mm/khugepaged.c:2297 > kthread+0x2e9/0x3a0 kernel/kthread.c:377 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > </TASK> > Modules linked in: > ---[ end trace 0000000000000000 ]--- > RIP: 0010:xa_parent_locked include/linux/xarray.h:1207 [inline] > RIP: 0010:xas_create_range+0x2d9/0x6e0 lib/xarray.c:725 > Code: 89 ee 49 83 ed 40 49 c1 ee 03 4c 89 6d 08 4c 8d 6d 12 4d 01 e6 e9 93 00 00 00 e8 d2 0f 72 fd 48 8d 7b 08 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 0f 85 fb 02 00 00 48 8b 04 24 4c 8b 7b 08 80 38 00 > RSP: 0018:ffffc90001097a48 EFLAGS: 00010002 > RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000000 > RDX: ffff8880139de240 RSI: ffffffff8405e5be RDI: 0000000000000008 > RBP: ffffc90001097bb0 R08: 0000000000000000 R09: 0000000000000000 > R10: ffffffff8405e679 R11: 0000000000000000 R12: dffffc0000000000 > R13: ffffc90001097bc2 R14: fffff52000212f76 R15: 0000000000000001 > FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007ffe25571c98 CR3: 0000000079206000 CR4: 00000000003506f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > ---------------- > Code disassembly (best guess): > 0: 89 ee mov %ebp,%esi > 2: 49 83 ed 40 sub $0x40,%r13 > 6: 49 c1 ee 03 shr $0x3,%r14 > a: 4c 89 6d 08 mov %r13,0x8(%rbp) > e: 4c 8d 6d 12 lea 0x12(%rbp),%r13 > 12: 4d 01 e6 add %r12,%r14 > 15: e9 93 00 00 00 jmpq 0xad > 1a: e8 d2 0f 72 fd callq 0xfd720ff1 > 1f: 48 8d 7b 08 lea 0x8(%rbx),%rdi > 23: 48 89 f8 mov %rdi,%rax > 26: 48 c1 e8 03 shr $0x3,%rax > * 2a: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1) <-- trapping instruction > 2f: 0f 85 fb 02 00 00 jne 0x330 > 35: 48 8b 04 24 mov (%rsp),%rax > 39: 4c 8b 7b 08 mov 0x8(%rbx),%r15 > 3d: 80 38 00 cmpb $0x0,(%rax) > > > --- > This report 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@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. >
