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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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