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Subject[PATCH 4.7 104/143] dm round robin: do not use this_cpu_ptr() without having preemption disabled
Date
4.7-stable review patch.  If anyone has any objections, please let me know.

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

From: Mike Snitzer <snitzer@redhat.com>

commit 802934b2cfde463b72cc1b9bc1c081895a90be53 upstream.

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

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

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