Messages in this thread Patch in this message | | | Date | Fri, 04 May 2012 13:43:21 -0700 | From | Greg KH <> | Subject | [ 57/75] exit_signal: simplify the "we have changed execution domain" logic |
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3.3-stable review patch. If anyone has any objections, please let me know.
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From: Oleg Nesterov <oleg@redhat.com>
commit e636825346b36a07ccfc8e30946d52855e21f681 upstream.
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> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/exec.c | 3 +++ kernel/exit.c | 7 +------ 2 files changed, 4 insertions(+), 6 deletions(-)
--- a/fs/exec.c +++ b/fs/exec.c @@ -975,6 +975,9 @@ static int de_thread(struct task_struct 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); --- a/kernel/exit.c +++ b/kernel/exit.c @@ -827,14 +827,9 @@ static void exit_notify(struct task_stru * 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)) {
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