KCSAN: data-race in ksys_write / ksys_write

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 94c00660 x86, kcsan: Enable KCSAN for x86
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=11203006e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=51a7c7d2972c87e5
dashboard link: https://syzkaller.appspot.com/bug?extid=0d3227815209510d83d8
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org
vi...@zeniv.linux.org.uk el...@google.com]

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+0d3227...@syzkaller.appspotmail.com

9pnet: Insufficient options for proto=fd
==================================================================
BUG: KCSAN: data-race in ksys_write / ksys_write

write to 0xffff8880a9c29568 of 8 bytes by task 27477 on cpu 1:
ksys_write+0x101/0x1b0 fs/read_write.c:613
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write fs/read_write.c:620 [inline]
__x64_sys_write+0x4c/0x60 fs/read_write.c:620
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880a9c29568 of 8 bytes by task 27475 on cpu 0:
ksys_write+0x101/0x1b0 fs/read_write.c:613
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write fs/read_write.c:620 [inline]
__x64_sys_write+0x4c/0x60 fs/read_write.c:620
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27475 Comm: syz-executor.0 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 27475 Comm: syz-executor.0 Not tainted 5.4.0-rc6+ #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+0xf5/0x159 lib/dump_stack.c:113
panic+0x210/0x640 kernel/panic.c:221
kcsan_report.cold+0xc/0xe kernel/kcsan/report.c:302
kcsan_setup_watchpoint+0x3fe/0x410 kernel/kcsan/core.c:357
check_access kernel/kcsan/core.c:409 [inline]
__tsan_unaligned_write8+0x143/0x1f0 kernel/kcsan/core.c:530
ksys_write+0x101/0x1b0 fs/read_write.c:613
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write fs/read_write.c:620 [inline]
__x64_sys_write+0x4c/0x60 fs/read_write.c:620
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45a219
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:00007f28e90a7c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a219
RDX: 0000000000000015 RSI: 0000000020000340 RDI: 0000000000000006
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f28e90a86d4
R13: 00000000004ca812 R14: 00000000004e2a78 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.