diff options
Diffstat (limited to 'kernel/signal.c')
| -rw-r--r-- | kernel/signal.c | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/kernel/signal.c b/kernel/signal.c index f7c6ffcbd044..f1ecd8f0c11d 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -435,6 +435,12 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags, * Preallocation does not hold sighand::siglock so it can't * use the cache. The lockless caching requires that only * one consumer and only one producer run at a time. + * + * For the regular allocation case it is sufficient to + * check @q for NULL because this code can only be called + * if the target task @t has not been reaped yet; which + * means this code can never observe the error pointer which is + * written to @t->sigqueue_cache in exit_task_sigqueue_cache(). */ q = READ_ONCE(t->sigqueue_cache); if (!q || sigqueue_flags) @@ -463,13 +469,18 @@ void exit_task_sigqueue_cache(struct task_struct *tsk) struct sigqueue *q = tsk->sigqueue_cache; if (q) { - tsk->sigqueue_cache = NULL; /* * Hand it back to the cache as the task might * be self reaping which would leak the object. */ kmem_cache_free(sigqueue_cachep, q); } + + /* + * Set an error pointer to ensure that @tsk will not cache a + * sigqueue when it is reaping it's child tasks + */ + tsk->sigqueue_cache = ERR_PTR(-1); } static void sigqueue_cache_or_free(struct sigqueue *q) @@ -481,6 +492,10 @@ static void sigqueue_cache_or_free(struct sigqueue *q) * is intentional when run without holding current->sighand->siglock, * which is fine as current obviously cannot run __sigqueue_free() * concurrently. + * + * The NULL check is safe even if current has been reaped already, + * in which case exit_task_sigqueue_cache() wrote an error pointer + * into current->sigqueue_cache. */ if (!READ_ONCE(current->sigqueue_cache)) WRITE_ONCE(current->sigqueue_cache, q); |