linux-kernel - [PATCH 4.7 104/143] dm round robin: do not use this_cpu

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Message-Id: <20160905164435.014029390@linuxfoundation.org>
Date:   Mon,  5 Sep 2016 18:44:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Benjamin Block <bblock@...ux.vnet.ibm.com>,
        Jens Axboe <axboe@...nel.dk>, Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 4.7 104/143] dm round robin: do not use this_cpu_ptr() without having preemption disabled

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Snitzer <snitzer@...hat.com>

commit 802934b2cfde463b72cc1b9bc1c081895a90be53 upstream.

Use local_irq_save() to disable preemption before calling
this_cpu_ptr().

Reported-by: Benjamin Block <bblock@...ux.vnet.ibm.com>
Fixes: b0b477c7e0dd ("dm round robin: use percpu 'repeat_count' and 'current_path'")
Suggested-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/dm-round-robin.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/md/dm-round-robin.c
+++ b/drivers/md/dm-round-robin.c
@@ -210,14 +210,17 @@ static struct dm_path *rr_select_path(st
 	struct path_info *pi = NULL;
 	struct dm_path *current_path = NULL;
 
+	local_irq_save(flags);
 	current_path = *this_cpu_ptr(s->current_path);
 	if (current_path) {
 		percpu_counter_dec(&s->repeat_count);
-		if (percpu_counter_read_positive(&s->repeat_count) > 0)
+		if (percpu_counter_read_positive(&s->repeat_count) > 0) {
+			local_irq_restore(flags);
 			return current_path;
+		}
 	}
 
-	spin_lock_irqsave(&s->lock, flags);
+	spin_lock(&s->lock);
 	if (!list_empty(&s->valid_paths)) {
 		pi = list_entry(s->valid_paths.next, struct path_info, list);
 		list_move_tail(&pi->list, &s->valid_paths);