[PATCH] Only send pdeath_signal when getppid changes.

Eric W. Biederman
2007-04-10T15:17:46Z

Currently each thread can requrest to be notified when it's parent
terminates, and receive a thread specific signal when that occurs.
That we set this on a per thread granularity and then send it to the
whole thread group seems silly, but whatever.

Currently we send a signal when the results of getppid don't change if
our parent thread dies and we are reparented to a different thread.
This seems counterintuitive to what I would expect when programming in
user space and is a major maitenance issue to continue doing.

The only users I recall using this have non threaded parents and
pdeath_signal predates CLONE_THREAD so arguably this code has been
broken with threaded parents since the day CLONE_THREAD was introduced
and no one ever screamed loudly enough to get it fixed.

So this patch fixes the pdeath_signal behaviour only sending a signal
when the results of getppid would change.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---

This patch is against 2.6.21-rc6-mm1 (with utrace applied)
but except for context in the diff that should not matter.

kernel/exit.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 1d91de8..1ec0d1f 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -618,10 +618,6 @@ choose_new_parent(struct task_struct *p, struct task_struct *reaper)
static void
reparent_thread(struct task_struct *p, struct task_struct *father)
{
- if (p->pdeath_signal)
- /* We already hold the tasklist_lock here. */
- group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
-
/* Move the child from its dying parent to the new one. */
list_move_tail(&p->sibling, &p->parent->children);

@@ -635,6 +631,10 @@ reparent_thread(struct task_struct *p, struct task_struct *father)
if (p->exit_signal != -1)
p->exit_signal = SIGCHLD;

+ if (p->pdeath_signal)
+ /* We already hold the tasklist_lock here. */
+ group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
+
/* If we'd notified the old parent about this child's death,
* also notify the new parent.
*/
--
1.5.0.g53756