Messages in this thread | | | Date | Wed, 15 Apr 2020 23:10:48 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCH 4/5] mm/swapfile: refcount block and queue before using blkcg_schedule_throttle() |
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On Wed, Apr 15, 2020 at 01:19:15PM +0000, Luis Chamberlain wrote: > > if (current->throttle_queue) > > return; > > + if (unlikely(current->flags & PF_KTHREAD)) > > + return; > > > > spin_lock(&swap_avail_lock); > > 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); > > - break; > > + if (!si->bdev) > > + continue; > > + if (blk_get_queue(dev_get_queue(si->bdev))) { > > + current->throttle_queue = dev_get_queue(si->bdev); > > + current->use_memdelay = true; > > + set_notify_resume(current); > > } > > + break; > > } > > spin_unlock(&swap_avail_lock); > > } > > Sorry, its not clear to me who calls the respective blk_put_queue() > here?
If you look at blkcg_schedule_throttle, it only puts the queue that was in current->throttle_queue. But mem_cgroup_throttle_swaprate exits early when current->throttle_queue is non-zero (first two lines quote above). So when called from mem_cgroup_throttle_swaprate, blkcg_schedule_throttle should never actually put a queue. Open coding the few relevant lines from blkcg_schedule_throttle in mem_cgroup_throttle_swaprate makes that obvious.
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