writeback: don't drain bdi_writeback_congested on bdi destruction
52ebea749a
("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:52ebea749a
("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>
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a13f35e871
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a20135ffbc
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@ -425,7 +425,6 @@ retry:
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new_congested = NULL;
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new_congested = NULL;
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rb_link_node(&congested->rb_node, parent, node);
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rb_link_node(&congested->rb_node, parent, node);
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rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
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rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
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atomic_inc(&bdi->usage_cnt);
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goto found;
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goto found;
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}
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}
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@ -456,7 +455,6 @@ found:
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*/
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*/
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void wb_congested_put(struct bdi_writeback_congested *congested)
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void wb_congested_put(struct bdi_writeback_congested *congested)
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{
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{
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struct backing_dev_info *bdi = congested->bdi;
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unsigned long flags;
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unsigned long flags;
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local_irq_save(flags);
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local_irq_save(flags);
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@ -465,12 +463,15 @@ void wb_congested_put(struct bdi_writeback_congested *congested)
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return;
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return;
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}
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}
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rb_erase(&congested->rb_node, &congested->bdi->cgwb_congested_tree);
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/* bdi might already have been destroyed leaving @congested unlinked */
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if (congested->bdi) {
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rb_erase(&congested->rb_node,
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&congested->bdi->cgwb_congested_tree);
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congested->bdi = NULL;
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}
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spin_unlock_irqrestore(&cgwb_lock, flags);
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spin_unlock_irqrestore(&cgwb_lock, flags);
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kfree(congested);
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kfree(congested);
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if (atomic_dec_and_test(&bdi->usage_cnt))
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wake_up_all(&cgwb_release_wait);
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}
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}
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static void cgwb_release_workfn(struct work_struct *work)
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static void cgwb_release_workfn(struct work_struct *work)
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@ -675,13 +676,22 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi)
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static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
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static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
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{
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{
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struct radix_tree_iter iter;
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struct radix_tree_iter iter;
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struct bdi_writeback_congested *congested, *congested_n;
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void **slot;
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void **slot;
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WARN_ON(test_bit(WB_registered, &bdi->wb.state));
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WARN_ON(test_bit(WB_registered, &bdi->wb.state));
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spin_lock_irq(&cgwb_lock);
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spin_lock_irq(&cgwb_lock);
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radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
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radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
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cgwb_kill(*slot);
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cgwb_kill(*slot);
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rbtree_postorder_for_each_entry_safe(congested, congested_n,
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&bdi->cgwb_congested_tree, rb_node) {
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rb_erase(&congested->rb_node, &bdi->cgwb_congested_tree);
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congested->bdi = NULL; /* mark @congested unlinked */
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}
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spin_unlock_irq(&cgwb_lock);
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spin_unlock_irq(&cgwb_lock);
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/*
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/*
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