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    Subject[PATCH 1/3] exit_signal: simplify the "we have changed execution domain" logic
    exit_notify() checks "tsk->self_exec_id != tsk->parent_exec_id"
    to handle the "we have changed execution domain" case.

    We can change do_thread() to always set ->exit_signal = SIGCHLD
    and remove this check to simplify the code.

    We could change setup_new_exec() instead, this looks more logical
    because it increments ->self_exec_id. But note that de_thread()
    already resets ->exit_signal if it changes the leader, let's keep
    both changes close to each other.

    Note that we change ->exit_signal lockless, this changes the rules.
    Thereafter ->exit_signal is not stable under tasklist but this is
    fine, the only possible change is OLDSIG -> SIGCHLD. This can race
    with eligible_child() but the race is harmless. We can race with
    reparent_leader() which changes our ->exit_signal in parallel, but
    it does the same change to SIGCHLD.

    The noticeable user-visible change is that the execing task is not
    "visible" to do_wait()->eligible_child(__WCLONE) right after exec.
    To me this looks more logical, and this is consistent with mt case.

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    ---
    fs/exec.c | 3 +++
    kernel/exit.c | 7 +------
    2 files changed, 4 insertions(+), 6 deletions(-)

    diff --git a/fs/exec.c b/fs/exec.c
    index 92ce83a..218d074 100644
    --- a/fs/exec.c
    +++ b/fs/exec.c
    @@ -975,6 +975,9 @@ static int de_thread(struct task_struct *tsk)
    sig->notify_count = 0;

    no_thread_group:
    + /* we have changed execution domain */
    + tsk->exit_signal = SIGCHLD;
    +
    if (current->mm)
    setmax_mm_hiwater_rss(&sig->maxrss, current->mm);

    diff --git a/kernel/exit.c b/kernel/exit.c
    index 7b36288..522c1aa 100644
    --- a/kernel/exit.c
    +++ b/kernel/exit.c
    @@ -827,14 +827,9 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
    * If the parent exec id doesn't match the exec id we saved
    * when we started then we know the parent has changed security
    * domain.
    - *
    - * If our self_exec id doesn't match our parent_exec_id then
    - * we have changed execution domain as these two values started
    - * the same after a fork.
    */
    if (thread_group_leader(tsk) && tsk->exit_signal != SIGCHLD &&
    - (tsk->parent_exec_id != tsk->real_parent->self_exec_id ||
    - tsk->self_exec_id != tsk->parent_exec_id))
    + tsk->parent_exec_id != tsk->real_parent->self_exec_id)
    tsk->exit_signal = SIGCHLD;

    if (unlikely(tsk->ptrace)) {
    --
    1.5.5.1



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