linux-kernel - [PATCH UPDATED 08/17] ptrace: use bit_waitqueue for TRAPPING instead of wait

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Date:	Thu, 2 Jun 2011 20:41:42 +0900
From:	Tejun Heo <tj@...nel.org>
To:	oleg@...hat.com
Cc:	vda.linux@...glemail.com, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu, bdonlan@...il.com,
	pedro@...esourcery.com
Subject: [PATCH UPDATED 08/17] ptrace: use bit_waitqueue for TRAPPING instead
 of wait_chldexit

>From abf3702a74e4e9f6fe4250bc82b80f8421b1dee3 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@...nel.org>
Date: Thu, 2 Jun 2011 11:14:00 +0200

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@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
---
Regenerated to apply on top of the updated first patch.  Other than
that, no change.

Thanks.

 kernel/ptrace.c |   10 ++++++++--
 kernel/signal.c |    3 +--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 0c37d99..7f05f3a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -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;
 }
 
diff --git a/kernel/signal.c b/kernel/signal.c
index 9ab91c5..172a4c7 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -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);
 	}
 }
 
-- 
1.7.5.2

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