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authorEric W. Biederman <ebiederm@xmission.com>2006-04-10 17:16:49 -0600
committerLinus Torvalds <torvalds@g5.osdl.org>2006-04-10 16:36:50 -0700
commitde12a7878c11f3b282d640888aa635e0711d0b5e (patch)
tree742b72a47cc36a7e591dba1883cd9af3c44290c4
parent1b72373491a061be6d456d219a4e2d054ac2aaad (diff)
[PATCH] de_thread: Don't confuse users do_each_thread.
Oleg Nesterov spotted two interesting bugs with the current de_thread code. The simplest is a long standing double decrement of __get_cpu_var(process_counts) in __unhash_process. Caused by two processes exiting when only one was created. The other is that since we no longer detach from the thread_group list it is possible for do_each_thread when run under the tasklist_lock to see the same task_struct twice. Once on the task list as a thread_group_leader, and once on the thread list of another thread. The double appearance in do_each_thread can cause a double increment of mm_core_waiters in zap_threads resulting in problems later on in coredump_wait. To remedy those two problems this patch takes the simple approach of changing the old thread group leader into a child thread. The only routine in release_task that cares is __unhash_process, and it can be trivially seen that we handle cleaning up a thread group leader properly. Since de_thread doesn't change the pid of the exiting leader process and instead shares it with the new leader process. I change thread_group_leader to recognize group leadership based on the group_leader field and not based on pids. This should also be slightly cheaper then the existing thread_group_leader macro. I performed a quick audit and I couldn't see any user of thread_group_leader that cared about the difference. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--fs/exec.c7
-rw-r--r--include/linux/sched.h3
2 files changed, 8 insertions, 2 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 0291a68a3626..4d38ad0b70d6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -723,7 +723,12 @@ static int de_thread(struct task_struct *tsk)
current->parent = current->real_parent = leader->real_parent;
leader->parent = leader->real_parent = child_reaper;
current->group_leader = current;
- leader->group_leader = leader;
+ leader->group_leader = current;
+
+ /* Reduce leader to a thread */
+ detach_pid(leader, PIDTYPE_PGID);
+ detach_pid(leader, PIDTYPE_SID);
+ list_del_init(&leader->tasks);
add_parent(current);
add_parent(leader);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 541f4828f5e7..a3e4f6b503a3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1203,7 +1203,8 @@ extern void wait_task_inactive(task_t * p);
#define while_each_thread(g, t) \
while ((t = next_thread(t)) != g)
-#define thread_group_leader(p) (p->pid == p->tgid)
+/* de_thread depends on thread_group_leader not being a pid based check */
+#define thread_group_leader(p) (p == p->group_leader)
static inline task_t *next_thread(task_t *p)
{