[PATCH] Fix fs/exec.c:788 (de_thread()) BUG_ON
It turns out that the BUG_ON() in fs/exec.c: de_thread() is unreliable
and can trigger due to the test itself being racy.
de_thread() does
while (atomic_read(&sig->count) > count) {
}
.....
.....
BUG_ON(!thread_group_empty(current));
but release_task does
write_lock_irq(&tasklist_lock)
__exit_signal
(this is where atomic_dec(&sig->count) is run)
__exit_sighand
__unhash_process
takes write lock on tasklist_lock
remove itself out of PIDTYPE_TGID list
write_unlock_irq(&tasklist_lock)
so there's a clear (although small) window between the
atomic_dec(&sig->count) and the actual PIDTYPE_TGID unhashing of the
thread.
And actually there is no need for all threads to have exited at this
point, so we simply kill the BUG_ON.
Big thanks to Marc Lehmann who provided the test-case.
Fixes Bug 5170 (http://bugme.osdl.org/show_bug.cgi?id=5170)
Signed-off-by: Alexander Nyberg <alexn@telia.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/exec.c b/fs/exec.c
index 14dd039..6fae59a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -745,8 +745,8 @@
}
/*
- * Now there are really no other threads at all,
- * so it's safe to stop telling them to kill themselves.
+ * There may be one thread left which is just exiting,
+ * but it's safe to stop telling the group to kill themselves.
*/
sig->flags = 0;
@@ -785,7 +785,6 @@
kmem_cache_free(sighand_cachep, oldsighand);
}
- BUG_ON(!thread_group_empty(current));
BUG_ON(!thread_group_leader(current));
return 0;
}