Re: [PATCH] ptrace: fix clearing of JOBCTL_TRACED in ptrace_unfreeze_traced()
From: Peter Zijlstra
Date: Wed Jul 06 2022 - 06:45:16 EST
On Wed, Jul 06, 2022 at 12:16:25PM +0200, Sven Schnelle wrote:
> CI reported the following splat while running the strace testsuite:
>
> [ 3976.640309] WARNING: CPU: 1 PID: 3570031 at kernel/ptrace.c:272 ptrace_check_attach+0x12e/0x178
> [ 3976.640391] CPU: 1 PID: 3570031 Comm: strace Tainted: G OE 5.19.0-20220624.rc3.git0.ee819a77d4e7.300.fc36.s390x #1
> [ 3976.640410] Hardware name: IBM 3906 M04 704 (z/VM 7.1.0)
> [ 3976.640452] Call Trace:
> [ 3976.640454] [<00000000ab4b645a>] ptrace_check_attach+0x132/0x178
> [ 3976.640457] ([<00000000ab4b6450>] ptrace_check_attach+0x128/0x178)
> [ 3976.640460] [<00000000ab4b6cde>] __s390x_sys_ptrace+0x86/0x160
> [ 3976.640463] [<00000000ac03fcec>] __do_syscall+0x1d4/0x200
> [ 3976.640468] [<00000000ac04e312>] system_call+0x82/0xb0
> [ 3976.640470] Last Breaking-Event-Address:
> [ 3976.640471] [<00000000ab4ea3c8>] wait_task_inactive+0x98/0x190
>
> This is because JOBCTL_TRACED is set, but the task is not in TASK_TRACED
> state. Caused by ptrace_unfreeze_traced() which does:
>
> task->jobctl &= ~TASK_TRACED
>
> but it should be:
>
> task->jobctl &= ~JOBCTL_TRACED
>
> Fixes: 31cae1eaae4f ("sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state")
> Signed-off-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
> kernel/ptrace.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 156a99283b11..1893d909e45c 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -222,7 +222,7 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
> if (lock_task_sighand(task, &flags)) {
> task->jobctl &= ~JOBCTL_PTRACE_FROZEN;
> if (__fatal_signal_pending(task)) {
> - task->jobctl &= ~TASK_TRACED;
> + task->jobctl &= ~JOBCTL_TRACED;
> wake_up_state(task, __TASK_TRACED);
> }
> unlock_task_sighand(task, &flags);
> --
> 2.34.1
>