KCSAN: data-race in get_signal / ptrace_check_attach (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: bdcf11de Merge tag 'riscv-for-linus-5.9-rc6' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11df7e9b900000
kernel config: https://syzkaller.appspot.com/x/.config?x=71d95d75ec48fd6f
dashboard link: https://syzkaller.appspot.com/bug?extid=670667eef68c9ab0c5fc
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
CC: [ax...@kernel.dk chri...@brauner.io ebie...@xmission.com linux-...@vger.kernel.org liuzhi...@huawei.com ol...@redhat.com]

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+670667...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in get_signal / ptrace_check_attach

write to 0xffff8880a7d364c8 of 8 bytes by task 27148 on cpu 0:
ptrace_signal kernel/signal.c:2489 [inline]
get_signal+0x86d/0x1650 kernel/signal.c:2653
arch_do_signal+0x25/0x270 arch/x86/kernel/signal.c:811
exit_to_user_mode_loop kernel/entry/common.c:159 [inline]
exit_to_user_mode_prepare+0x124/0x210 kernel/entry/common.c:190
syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:265
do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a7d364c8 of 8 bytes by task 27152 on cpu 1:
ptrace_freeze_traced kernel/ptrace.c:178 [inline]
ptrace_check_attach+0xd8/0x220 kernel/ptrace.c:247
__do_sys_ptrace kernel/ptrace.c:1272 [inline]
__se_sys_ptrace+0xdb/0x2d0 kernel/ptrace.c:1242
__x64_sys_ptrace+0x51/0x60 kernel/ptrace.c:1242
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 27152 Comm: syz-executor.4 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 27152 Comm: syz-executor.4 Not tainted 5.9.0-rc5-syzkaller #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+0x10f/0x19d lib/dump_stack.c:118
panic+0x207/0x64a kernel/panic.c:231
kcsan_report+0x684/0x690 kernel/kcsan/report.c:630
kcsan_setup_watchpoint+0x41e/0x4a0 kernel/kcsan/core.c:540
ptrace_freeze_traced kernel/ptrace.c:178 [inline]
ptrace_check_attach+0xd8/0x220 kernel/ptrace.c:247
__do_sys_ptrace kernel/ptrace.c:1272 [inline]
__se_sys_ptrace+0xdb/0x2d0 kernel/ptrace.c:1242
__x64_sys_ptrace+0x51/0x60 kernel/ptrace.c:1242
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d5f9
Code: 5d b4 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 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb2c5740c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000065
RAX: ffffffffffffffda RBX: 0000000000025b80 RCX: 000000000045d5f9
RDX: 0000000000000000 RSI: 0000000000000610 RDI: 0000000000000007
RBP: 000000000118cf88 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007ffe059f03ff R14: 00007fb2c57419c0 R15: 000000000118cf4c
Shutting down cpus with NMI
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.