[PATCH block/for-linus] blkcg: Fix multiple bugs in blkcg_activate_policy()

Tejun Heo
2019-10-15T16:03:54Z

blkcg_activate_policy() has the following bugs.

* cf09a8ee19ad ("blkcg: pass @q and @blkcg into
blkcg_pol_alloc_pd_fn()") added @blkcg to ->pd_alloc_fn(); however,
blkcg_activate_policy() ends up using pd's allocated for the root
blkcg for all preallocations, so ->pd_init_fn() for non-root blkcgs
can be passed in pd's which are allocated for the root blkcg.

For blk-iocost, this means that ->pd_init_fn() can write beyond the
end of the allocated object as it determines the length of the flex
array at the end based on the blkcg's nesting level.

* Each pd is initialized as they get allocated. If alloc fails, the
policy will get freed with pd's initialized on it.

* After the above partial failure, the partial pds are not freed.

This patch fixes all the above issues by

* Restructuring blkcg_activate_policy() so that alloc and init passes
are separate. Init takes place only after all allocs succeeded and
on failure all allocated pds are freed.

* Unifying and fixing the cleanup of the remaining pd_prealloc.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: cf09a8ee19ad ("blkcg: pass @q and @blkcg into blkcg_pol_alloc_pd_fn()")
---
block/blk-cgroup.c | 69 +++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 51 insertions(+), 18 deletions(-)

--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1362,7 +1362,7 @@ int blkcg_activate_policy(struct request
const struct blkcg_policy *pol)
{
struct blkg_policy_data *pd_prealloc = NULL;
- struct blkcg_gq *blkg;
+ struct blkcg_gq *blkg, *pinned_blkg = NULL;
int ret;

if (blkcg_policy_enabled(q, pol))
@@ -1370,49 +1370,82 @@ int blkcg_activate_policy(struct request

if (queue_is_mq(q))
blk_mq_freeze_queue(q);
-pd_prealloc:
- if (!pd_prealloc) {
- pd_prealloc = pol->pd_alloc_fn(GFP_KERNEL, q, &blkcg_root);
- if (!pd_prealloc) {
- ret = -ENOMEM;
- goto out_bypass_end;
- }
- }
-
+retry:
spin_lock_irq(&q->queue_lock);

- /* blkg_list is pushed at the head, reverse walk to init parents first */
+ /* blkg_list is pushed at the head, reverse walk to allocate parents first */
list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
struct blkg_policy_data *pd;

if (blkg->pd[pol->plid])
continue;

- pd = pol->pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN, q, &blkcg_root);
- if (!pd)
- swap(pd, pd_prealloc);
+ /* If prealloc matches, use it; otherwise try GFP_NOWAIT */
+ if (blkg == pinned_blkg) {
+ pd = pd_prealloc;
+ pd_prealloc = NULL;
+ } else {
+ pd = pol->pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN, q,
+ blkg->blkcg);
+ }
+
if (!pd) {
+ /*
+ * GFP_NOWAIT failed. Free the existing one and
+ * prealloc for @blkg w/ GFP_KERNEL.
+ */
+ if (pinned_blkg)
+ blkg_put(pinned_blkg);
+ blkg_get(blkg);
+ pinned_blkg = blkg;
+
spin_unlock_irq(&q->queue_lock);
- goto pd_prealloc;
+
+ if (pd_prealloc)
+ pol->pd_free_fn(pd_prealloc);
+ pd_prealloc = pol->pd_alloc_fn(GFP_KERNEL, q,
+ blkg->blkcg);
+ if (pd_prealloc)
+ goto retry;
+ else
+ goto enomem;
}

blkg->pd[pol->plid] = pd;
pd->blkg = blkg;
pd->plid = pol->plid;
- if (pol->pd_init_fn)
- pol->pd_init_fn(pd);
}

+ /* all allocated, init in the same order */
+ if (pol->pd_init_fn)
+ list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
+ pol->pd_init_fn(blkg->pd[pol->plid]);
+
__set_bit(pol->plid, q->blkcg_pols);
ret = 0;

spin_unlock_irq(&q->queue_lock);
-out_bypass_end:
+out:
if (queue_is_mq(q))
blk_mq_unfreeze_queue(q);
+ if (pinned_blkg)
+ blkg_put(pinned_blkg);
if (pd_prealloc)
pol->pd_free_fn(pd_prealloc);
return ret;
+
+enomem:
+ /* alloc failed, nothing's initialized yet, free everything */
+ spin_lock_irq(&q->queue_lock);
+ list_for_each_entry(blkg, &q->blkg_list, q_node) {
+ if (blkg->pd[pol->plid]) {
+ pol->pd_free_fn(blkg->pd[pol->plid]);
+ blkg->pd[pol->plid] = NULL;
+ }
+ }
+ spin_unlock_irq(&q->queue_lock);
+ ret = -ENOMEM;
+ goto out;
}
EXPORT_SYMBOL_GPL(blkcg_activate_policy);