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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@kernel.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@kernel.org>
Cc: Linus Torvalds <torvalds@linux-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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