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ptrace: use bit_waitqueue for TRAPPING instead of wait_chldexit

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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>
This commit is contained in:
Tejun Heo 2011-06-02 11:14:00 +02:00 committed by Oleg Nesterov
parent 7dd3db54e7
commit 62c124ff3b
2 changed files with 9 additions and 4 deletions
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10
kernel/ptrace.c
View File

@ -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;
}

3
kernel/signal.c
View File

@ -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);
}
}