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Commit 23b5d9f8 authored by Vinayak Menon's avatar Vinayak Menon
Browse files

mm: process_reclaim: do not iterate over stale task structs 



swap_fn iterates through the threads of selected tasks after
a rcu_read_unlock which is wrong. But we can't extend the
rcu_read_lock since it will result in severe performance
issues. So better avoid iterating over the threads. Just
lock the group leader and use it further.

Change-Id: I36269b1b6619315f33f6f3b49ec73571a66796f2
Signed-off-by: default avatarVinayak Menon <vinmenon@codeaurora.org>
parent a9ee5f7d

mm/process_reclaim.c

+12 −19
Original line number Diff line number Diff line
@@ -88,14 +88,17 @@ static int test_task_flag(struct task_struct *p, int flag) 
{

	struct task_struct *t = p;



	do {

	rcu_read_lock();

	for_each_thread(p, t) {

		task_lock(t);

		if (test_tsk_thread_flag(t, flag)) {

			task_unlock(t);

			rcu_read_unlock();

			return 1;

		}

		task_unlock(t);

	} while_each_thread(p, t);

	}

	rcu_read_unlock();



	return 0;

}
@@ -125,10 +128,6 @@ static void swap_fn(struct work_struct *work) 
		if (tsk->flags & PF_KTHREAD)

			continue;



		/* if task no longer has any memory ignore it */

		if (test_task_flag(tsk, TIF_MM_RELEASED))

			continue;



		if (test_task_flag(tsk, TIF_MEMDIE))

			continue;
@@ -165,20 +164,20 @@ static void swap_fn(struct work_struct *work) 
		}

	}



	for (i = 0; i < si; i++) {

		get_task_struct(selected[i].p);

	for (i = 0; i < si; i++)

		total_sz += selected[i].tasksize;

	}



	rcu_read_unlock();



	/* Skip reclaim if total size is too less */

	if (total_sz < SWAP_CLUSTER_MAX) {

		for (i = 0; i < si; i++)

			put_task_struct(selected[i].p);

		rcu_read_unlock();

		return;

	}



	for (i = 0; i < si; i++)

		get_task_struct(selected[i].p);



	rcu_read_unlock();



	while (si--) {

		nr_to_reclaim =

			(selected[si].tasksize * per_swap_size) / total_sz;
@@ -186,12 +185,6 @@ static void swap_fn(struct work_struct *work) 
		if (!nr_to_reclaim)

			nr_to_reclaim = 1;



		if ((test_task_flag(selected[si].p, TIF_MM_RELEASED))

			|| (test_task_flag(selected[si].p, TIF_MEMDIE))) {

			put_task_struct(selected[si].p);

			continue;

		}



		rp = reclaim_task_anon(selected[si].p, nr_to_reclaim);



		trace_process_reclaim(selected[si].tasksize,