goto repeat;
}
+/*
+ * Note that if this function returns a valid task_struct pointer (!NULL)
+ * task->usage must remain >0 for the duration of the RCU critical section.
+ */
+struct task_struct *task_rcu_dereference(struct task_struct **ptask)
+{
+ struct sighand_struct *sighand;
+ struct task_struct *task;
+
+ /*
+ * We need to verify that release_task() was not called and thus
+ * delayed_put_task_struct() can't run and drop the last reference
+ * before rcu_read_unlock(). We check task->sighand != NULL,
+ * but we can read the already freed and reused memory.
+ */
+retry:
+ task = rcu_dereference(*ptask);
+ if (!task)
+ return NULL;
+
+ probe_kernel_address(&task->sighand, sighand);
+
+ /*
+ * Pairs with atomic_dec_and_test() in put_task_struct(). If this task
+ * was already freed we can not miss the preceding update of this
+ * pointer.
+ */
+ smp_rmb();
+ if (unlikely(task != READ_ONCE(*ptask)))
+ goto retry;
+
+ /*
+ * We've re-checked that "task == *ptask", now we have two different
+ * cases:
+ *
+ * 1. This is actually the same task/task_struct. In this case
+ * sighand != NULL tells us it is still alive.
+ *
+ * 2. This is another task which got the same memory for task_struct.
+ * We can't know this of course, and we can not trust
+ * sighand != NULL.
+ *
+ * In this case we actually return a random value, but this is
+ * correct.
+ *
+ * If we return NULL - we can pretend that we actually noticed that
+ * *ptask was updated when the previous task has exited. Or pretend
+ * that probe_slab_address(&sighand) reads NULL.
+ *
+ * If we return the new task (because sighand is not NULL for any
+ * reason) - this is fine too. This (new) task can't go away before
+ * another gp pass.
+ *
+ * And note: We could even eliminate the false positive if re-read
+ * task->sighand once again to avoid the falsely NULL. But this case
+ * is very unlikely so we don't care.
+ */
+ if (!sighand)
+ return NULL;
+
+ return task;
+}
+
+struct task_struct *try_get_task_struct(struct task_struct **ptask)
+{
+ struct task_struct *task;
+
+ rcu_read_lock();
+ task = task_rcu_dereference(ptask);
+ if (task)
+ get_task_struct(task);
+ rcu_read_unlock();
+
+ return task;
+}
+
/*
* Determine if a process group is "orphaned", according to the POSIX
* definition in 2.2.2.52. Orphaned process groups are not to be affected
exit_signals(tsk); /* sets PF_EXITING */
/*
- * tsk->flags are checked in the futex code to protect against
- * an exiting task cleaning up the robust pi futexes.
+ * Ensure that all new tsk->pi_lock acquisitions must observe
+ * PF_EXITING. Serializes against futex.c:attach_to_pi_owner().
*/
smp_mb();
+ /*
+ * Ensure that we must observe the pi_state in exit_mm() ->
+ * mm_release() -> exit_pi_state_list().
+ */
raw_spin_unlock_wait(&tsk->pi_lock);
if (unlikely(in_atomic())) {
disassociate_ctty(1);
exit_task_namespaces(tsk);
exit_task_work(tsk);
- exit_thread();
+ exit_thread(tsk);
/*
* Flush inherited counters to the parent - before the parent
task_pid_type(p, wo->wo_type) == wo->wo_pid;
}
-static int eligible_child(struct wait_opts *wo, struct task_struct *p)
+static int
+eligible_child(struct wait_opts *wo, bool ptrace, struct task_struct *p)
{
if (!eligible_pid(wo, p))
return 0;
- /* Wait for all children (clone and not) if __WALL is set;
- * otherwise, wait for clone children *only* if __WCLONE is
- * set; otherwise, wait for non-clone children *only*. (Note:
- * A "clone" child here is one that reports to its parent
- * using a signal other than SIGCHLD.) */
- if (((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
- && !(wo->wo_flags & __WALL))
+
+ /*
+ * Wait for all children (clone and not) if __WALL is set or
+ * if it is traced by us.
+ */
+ if (ptrace || (wo->wo_flags & __WALL))
+ return 1;
+
+ /*
+ * Otherwise, wait for clone children *only* if __WCLONE is set;
+ * otherwise, wait for non-clone children *only*.
+ *
+ * Note: a "clone" child here is one that reports to its parent
+ * using a signal other than SIGCHLD, or a non-leader thread which
+ * we can only see if it is traced by us.
+ */
+ if ((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
return 0;
return 1;
if (unlikely(exit_state == EXIT_DEAD))
return 0;
- ret = eligible_child(wo, p);
+ ret = eligible_child(wo, ptrace, p);
if (!ret)
return ret;
enum pid_type type;
long ret;
- if (options & ~(WNOHANG|WNOWAIT|WEXITED|WSTOPPED|WCONTINUED))
+ if (options & ~(WNOHANG|WNOWAIT|WEXITED|WSTOPPED|WCONTINUED|
+ __WNOTHREAD|__WCLONE|__WALL))
return -EINVAL;
if (!(options & (WEXITED|WSTOPPED|WCONTINUED)))
return -EINVAL;
projects / karo-tx-linux.git / blobdiff