ptrace_attach() can hang waiting for STOPPED -> TRACED transition if the tracee gets frozen in between, change wait_on_bit() to use TASK_KILLABLE.
This doesn't really solve the problem(s) and we probably need to fix the freezer. In particular, note that this means that pm freezer will fail if it races attach-to-stopped-task. And otoh perhaps we can just remove JOBCTL_TRAPPING_BIT altogether, it is not clear if we really need to hide this transition from debugger, WNOHANG after PTRACE_ATTACH can fail anyway if it races with SIGCONT. Reported-by: Andrey Ryabinin <[email protected]> Signed-off-by: Oleg Nesterov <[email protected]> --- kernel/ptrace.c | 10 ++++++++-- 1 files changed, 8 insertions(+), 2 deletions(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index c8e0e05..80b3604 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -364,8 +364,14 @@ unlock_creds: mutex_unlock(&task->signal->cred_guard_mutex); out: if (!retval) { - wait_on_bit(&task->jobctl, JOBCTL_TRAPPING_BIT, - TASK_UNINTERRUPTIBLE); + /* + * We do not bother to change retval or clear JOBCTL_TRAPPING + * if wait_on_bit() was interrupted by SIGKILL. The tracer will + * not return to user-mode, it will exit and clear this bit in + * __ptrace_unlink() if it wasn't already cleared by the tracee; + * and until then nobody can ptrace this task. + */ + wait_on_bit(&task->jobctl, JOBCTL_TRAPPING_BIT, TASK_KILLABLE); proc_ptrace_connector(task, PTRACE_ATTACH); } -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
