KCSAN: data-race in prepare_signal / ptrace

KCSAN: data-race in prepare_signal / ptrace_attach (3)
Status: auto-closed as invalid on 2021/03/01 09:38
Reported-by: syzbot+@syzkaller.appspotmail.com
First crash: 220d, last: 186d

similar bugs (3):
Kernel	Title	Count	Last	Reported	Patched	Status
upstream	KCSAN: data-race in prepare_signal / ptrace_attach	1	401d	401d	0/22	auto-closed as invalid on 2020/07/29 00:33
upstream	KCSAN: data-race in prepare_signal / ptrace_attach (2)	3	325d	360d	0/22	auto-closed as invalid on 2020/10/13 05:51
upstream	KCSAN: data-race in prepare_signal / ptrace_attach (4)	1	92d	92d	0/22	auto-closed as invalid on 2021/06/03 07:49

Sample crash report:

==================================================================
BUG: KCSAN: data-race in prepare_signal / ptrace_attach

write to 0xffff88802aaac030 of 4 bytes by task 20231 on cpu 0:
 ptrace_attach+0x217/0x4b0 kernel/ptrace.c:407
 __do_sys_ptrace kernel/ptrace.c:1256 [inline]
 __se_sys_ptrace+0xc1/0x2e0 kernel/ptrace.c:1236
 __x64_sys_ptrace+0x51/0x60 kernel/ptrace.c:1236
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88802aaac030 of 4 bytes by task 20236 on cpu 1:
 sig_ignored kernel/signal.c:116 [inline]
 prepare_signal+0x769/0xd80 kernel/signal.c:962
 __send_signal+0x64/0x780 kernel/signal.c:1082
 send_signal+0x39f/0x3d0 kernel/signal.c:1242
 do_send_sig_info+0x9b/0xe0 kernel/signal.c:1291
 do_send_specific kernel/signal.c:3819 [inline]
 do_tkill kernel/signal.c:3845 [inline]
 __do_sys_tkill kernel/signal.c:3880 [inline]
 __se_sys_tkill+0x12b/0x180 kernel/signal.c:3874
 __x64_sys_tkill+0x2d/0x40 kernel/signal.c:3874
 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: 20236 Comm: syz-executor.5 Not tainted 5.11.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================

Crashes (2):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Title
ci2-upstream-kcsan-gce	2021/01/25 09:31	upstream	6ee1d745b7c9	52e37319	.config	log	report			info	KCSAN: data-race in prepare_signal / ptrace_attach
ci2-upstream-kcsan-gce	2020/12/21 21:01	upstream	e37b12e4bb21	04201c06	.config	log	report			info