KCSAN: data-race in do_signal_stop / task_set_jobctl_pending

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7c3cd68e Merge remote-tracking branch 'linux-rcu/kcsan' in..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=11494f19100000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff291dc25f22cdda
dashboard link: https://syzkaller.appspot.com/bug?extid=80062d8928a222cd4f43
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [ak...@linux-foundation.org chri...@brauner.io ebie...@xmission.com jo...@joelfernandes.org linux-...@vger.kernel.org ol...@redhat.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+80062d...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_signal_stop / task_set_jobctl_pending

write to 0xffff888033564024 of 4 bytes by task 20391 on cpu 0:
freezer_count include/linux/freezer.h:121 [inline]
freezable_schedule include/linux/freezer.h:173 [inline]
do_signal_stop+0x1f0/0x4e0 kernel/signal.c:2395
get_signal+0xa8f/0x1290 kernel/signal.c:2597
do_signal+0x2b/0x840 arch/x86/kernel/signal.c:784
exit_to_usermode_loop+0x24a/0x2c0 arch/x86/entry/common.c:161
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x38b/0x3b0 arch/x86/entry/common.c:305
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888033564024 of 4 bytes by task 20386 on cpu 1:
task_set_jobctl_pending+0x98/0x180 kernel/signal.c:291
do_signal_stop+0x3f7/0x4e0 kernel/signal.c:2354
get_signal+0x601/0x1290 kernel/signal.c:2699
do_signal+0x2b/0x840 arch/x86/kernel/signal.c:784
exit_to_usermode_loop+0x24a/0x2c0 arch/x86/entry/common.c:161
prepare_exit_to_usermode+0x194/0x1e0 arch/x86/entry/common.c:196
swapgs_restore_regs_and_return_to_usermode+0x0/0x40

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 20386 Comm: syz-executor.0 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

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