writeback: don't drain bdi_writeback_congested on bdi destruction
52ebea749aae ("writeback: make backing_dev_info host cgroup-specific
bdi_writebacks") made bdi (backing_dev_info) host per-cgroup wb's
(bdi_writeback's). As the congested state needs to be per-wb and
referenced from blkcg side and multiple wbs, the patch made all
non-root cong's (bdi_writeback_congested's) reference counted and
indexed on bdi.
When a bdi is destroyed, cgwb_bdi_destroy() tries to drain all
non-root cong's; however, this can hang indefinitely because wb's can
also be referenced from blkcg_gq's which are destroyed after bdi
destruction is complete.
This patch fixes the bug by updating bdi destruction to not wait for
cong's to drain. A cong is unlinked from bdi->cgwb_congested_tree on
bdi destuction regardless of its reference count as the bdi may go
away any point after destruction. wb_congested_put() checks whether
the cong is already unlinked on release.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jon Christopherson <jon@jons.org>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=100681
Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks")
Tested-by: Jon Christopherson <jon@jons.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 51cc461..dac5bf5 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -425,7 +425,6 @@
new_congested = NULL;
rb_link_node(&congested->rb_node, parent, node);
rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
- atomic_inc(&bdi->usage_cnt);
goto found;
}
@@ -456,7 +455,6 @@
*/
void wb_congested_put(struct bdi_writeback_congested *congested)
{
- struct backing_dev_info *bdi = congested->bdi;
unsigned long flags;
local_irq_save(flags);
@@ -465,12 +463,15 @@
return;
}
- rb_erase(&congested->rb_node, &congested->bdi->cgwb_congested_tree);
+ /* bdi might already have been destroyed leaving @congested unlinked */
+ if (congested->bdi) {
+ rb_erase(&congested->rb_node,
+ &congested->bdi->cgwb_congested_tree);
+ congested->bdi = NULL;
+ }
+
spin_unlock_irqrestore(&cgwb_lock, flags);
kfree(congested);
-
- if (atomic_dec_and_test(&bdi->usage_cnt))
- wake_up_all(&cgwb_release_wait);
}
static void cgwb_release_workfn(struct work_struct *work)
@@ -675,13 +676,22 @@
static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
{
struct radix_tree_iter iter;
+ struct bdi_writeback_congested *congested, *congested_n;
void **slot;
WARN_ON(test_bit(WB_registered, &bdi->wb.state));
spin_lock_irq(&cgwb_lock);
+
radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
cgwb_kill(*slot);
+
+ rbtree_postorder_for_each_entry_safe(congested, congested_n,
+ &bdi->cgwb_congested_tree, rb_node) {
+ rb_erase(&congested->rb_node, &bdi->cgwb_congested_tree);
+ congested->bdi = NULL; /* mark @congested unlinked */
+ }
+
spin_unlock_irq(&cgwb_lock);
/*