Commit a20135ff authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe

writeback: don't drain bdi_writeback_congested on bdi destruction

52ebea74 ("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: default avatarTejun Heo <tj@kernel.org>
Reported-by: default avatarJon Christopherson <jon@jons.org>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=100681
Fixes: 52ebea74 ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks")
Tested-by: default avatarJon Christopherson <jon@jons.org>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent a13f35e8
...@@ -425,7 +425,6 @@ retry: ...@@ -425,7 +425,6 @@ retry:
new_congested = NULL; new_congested = NULL;
rb_link_node(&congested->rb_node, parent, node); rb_link_node(&congested->rb_node, parent, node);
rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree); rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
atomic_inc(&bdi->usage_cnt);
goto found; goto found;
} }
...@@ -456,7 +455,6 @@ found: ...@@ -456,7 +455,6 @@ found:
*/ */
void wb_congested_put(struct bdi_writeback_congested *congested) void wb_congested_put(struct bdi_writeback_congested *congested)
{ {
struct backing_dev_info *bdi = congested->bdi;
unsigned long flags; unsigned long flags;
local_irq_save(flags); local_irq_save(flags);
...@@ -465,12 +463,15 @@ void wb_congested_put(struct bdi_writeback_congested *congested) ...@@ -465,12 +463,15 @@ void wb_congested_put(struct bdi_writeback_congested *congested)
return; 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); spin_unlock_irqrestore(&cgwb_lock, flags);
kfree(congested); 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) static void cgwb_release_workfn(struct work_struct *work)
...@@ -675,13 +676,22 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi) ...@@ -675,13 +676,22 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi)
static void cgwb_bdi_destroy(struct backing_dev_info *bdi) static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
{ {
struct radix_tree_iter iter; struct radix_tree_iter iter;
struct bdi_writeback_congested *congested, *congested_n;
void **slot; void **slot;
WARN_ON(test_bit(WB_registered, &bdi->wb.state)); WARN_ON(test_bit(WB_registered, &bdi->wb.state));
spin_lock_irq(&cgwb_lock); spin_lock_irq(&cgwb_lock);
radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0) radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
cgwb_kill(*slot); 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); spin_unlock_irq(&cgwb_lock);
/* /*
......
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