depends on
"[PATCH rc1-mm] de_thread: fix deadlockable process addition"
This patch removes tasklist_lock from zap_threads().
This is safe wrt:
do_exit:
The caller holds mm->mmap_sem. This means that task which
shares the same ->mm can't pass exit_mm(), so it can't be
unhashed from init_task.tasks or ->thread_group lists.
fork:
None of sub-threads can fork after zap_process(leader). All
processes which were created before this point should be
visible to zap_threads() because copy_process() adds the new
process to the tail of init_task.tasks list, and ->siglock
lock/unlock provides a memory barrier.
de_thread:
It does list_replace_rcu(&leader->tasks, ¤t->tasks).
So zap_threads() will see either old or new leader, it does
not matter. However, it can change p->sighand, so we should
use lock_task_sighand() in zap_process().
Signed-off-by: Oleg Nesterov <[email protected]>
--- MM/fs/exec.c~4_TLOCK 2006-04-07 01:21:41.000000000 +0400
+++ MM/fs/exec.c 2006-04-07 01:32:02.000000000 +0400
@@ -1385,7 +1385,11 @@ static void zap_process(struct task_stru
struct task_struct *t;
unsigned long flags;
- spin_lock_irqsave(&start->sighand->siglock, flags);
+ /*
+ * start->sighand can't disappear, but may be
+ * changed by de_thread()
+ */
+ lock_task_sighand(start, &flags);
start->signal->flags = SIGNAL_GROUP_EXIT;
start->signal->group_stop_count = 0;
@@ -1398,7 +1402,7 @@ static void zap_process(struct task_stru
}
} while ((t = next_thread(t)) != start);
- spin_unlock_irqrestore(&start->sighand->siglock, flags);
+ unlock_task_sighand(start, &flags);
}
static void zap_threads(struct mm_struct *mm)
@@ -1416,7 +1420,7 @@ static void zap_threads(struct mm_struct
complete(vfork_done);
}
- read_lock(&tasklist_lock);
+ rcu_read_lock();
for_each_process(g) {
p = g;
do {
@@ -1427,7 +1431,7 @@ static void zap_threads(struct mm_struct
}
} while ((p = next_thread(p)) != g);
}
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
}
static void coredump_wait(struct mm_struct *mm)
-
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