Commit 62c124ff authored Jun 02, 2011 by Tejun Heo Committed by Oleg Nesterov Jun 04, 2011

ptrace: use bit_waitqueue for TRAPPING instead of wait_chldexit



ptracer->signal->wait_chldexit was used to wait for TRAPPING; however,
->wait_chldexit was already complicated with waker-side filtering
without adding TRAPPING wait on top of it.  Also, it unnecessarily
made TRAPPING clearing depend on the current ptrace relationship - if
the ptracee is detached, wakeup is lost.

There is no reason to use signal->wait_chldexit here.  We're just
waiting for JOBCTL_TRAPPING bit to clear and given the relatively
infrequent use of ptrace, bit_waitqueue can serve it perfectly.

This patch makes JOBCTL_TRAPPING wait use bit_waitqueue instead of
signal->wait_chldexit.

-v2: Use JOBCTL_*_BIT macros instead of ilog2() as suggested by Linus.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>

parent 7dd3db54

kernel/ptrace.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -25,6 +25,12 @@
		#include <linux/hw_breakpoint.h>


		static int ptrace_trapping_sleep_fn(void *flags)
		{
		schedule();
		return 0;
		}

		/*
		* ptrace a task: make the debugger its new parent and
		* move it to the ptrace list.
		@@ -270,8 +276,8 @@ unlock_creds:
		mutex_unlock(&task->signal->cred_guard_mutex);
		out:
		if (!retval)
		wait_event(current->signal->wait_chldexit,
		!(task->jobctl & JOBCTL_TRAPPING));
		wait_on_bit(&task->jobctl, JOBCTL_TRAPPING_BIT,
		ptrace_trapping_sleep_fn, TASK_UNINTERRUPTIBLE);
		return retval;
		}

kernel/signal.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -272,8 +272,7 @@ static void task_clear_jobctl_trapping(struct task_struct *task)
		{
		if (unlikely(task->jobctl & JOBCTL_TRAPPING)) {
		task->jobctl &= ~JOBCTL_TRAPPING;
		__wake_up_sync_key(&task->parent->signal->wait_chldexit,
		TASK_UNINTERRUPTIBLE, 1, task);
		wake_up_bit(&task->jobctl, JOBCTL_TRAPPING_BIT);
		}
		}

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