From 7c3b00e06d731a28fc3d17ed02ba250642b15b81 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 20 Jan 2016 14:59:55 -0800 Subject: [PATCH] ptrace: make wait_on_bit(JOBCTL_TRAPPING_BIT) in ptrace_attach() killable 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. Signed-off-by: Oleg Nesterov Reported-by: Andrey Ryabinin Cc: Roland McGrath Acked-by: Tejun Heo Cc: Pedro Alves Cc: Jan Kratochvil Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/ptrace.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index b760bae64cf1..aa94aee9d4c9 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); } -- 2.20.1