block devices are refcounted so to ensure once its final user goes away it
can be cleaned up by the lower layers properly. The block device's
request_queue structure is also refcounted, however, if the last
blk_put_queue() is called under atomic context the block layer has
to defer removal.
By refcounting the block device during the use of blkcg_schedule_throttle(),
we ensure ensure two things:
1) the block device remains available during the call
2) we ensure avoid having to deal with the fact we're using the
request_queue structure in atomic context, since the last
blk_put_queue() will be called upon disk_release(), *after*
our own bdput().
This means this code path is *not* going to remove the request_queue
structure, as we are ensuring some later upper layer disk_release()
will be the one to release the request_queue structure for us.
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Omar Sandoval <osandov@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Nicolai Stange <nstange@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: yu kuai <yukuai3@xxxxxxxxxx>
Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
---
mm/swapfile.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6659ab563448..9285ff6030ca 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3753,6 +3753,7 @@ static void free_swap_count_continuations(struct swap_info_struct *si)
void mem_cgroup_throttle_swaprate(struct mem_cgroup *memcg, int node,
gfp_t gfp_mask)
{
+ struct block_device *bdev;
struct swap_info_struct *si, *next;
if (!(gfp_mask & __GFP_IO) || !memcg)
return;
@@ -3771,8 +3772,17 @@ void mem_cgroup_throttle_swaprate(struct mem_cgroup *memcg, int node,
plist_for_each_entry_safe(si, next, &swap_avail_heads[node],
avail_lists[node]) {
if (si->bdev) {
- blkcg_schedule_throttle(bdev_get_queue(si->bdev),
- true);
+ bdev = bdgrab(si->bdev);
+ if (!bdev)
+ continue;
+ /*
+ * By adding our own bdgrab() we ensure the queue
+ * sticks around until disk_release(), and so we ensure
+ * our release of the request_queue does not happen in
+ * atomic context.
+ */
+ blkcg_schedule_throttle(bdev_get_queue(bdev), true);
+ bdput(bdev);
break;
}
}
--
2.25.1
