[PATCH block/for-linus] blkcg: fix botched pd_prealloc error handling in blkcg_activate_policy()

Tejun Heo
2019-10-15T15:48:33Z

While fixing ->pd_alloc_fn() bug, ab94b0382d81 ("blkcg: Fix
->pd_alloc_fn() being called with the wrong blkcg on policy
activation") broke the pd_prealloc error handling.

* pd's were freed using kfree(). They should be freed with
->pd_free_fn().

* pd_prealloc could be kfree()'d and then ->pd_free_fn()'d again.

* When GFP_KERNEL allocation fails, pinned_blkg wasn't put.

There are also a couple existing issues.

* 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 of the above issues.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Fixes: ab94b0382d81 ("blkcg: Fix ->pd_alloc_fn() being called with the wrong blkcg on policy activation")
---
block/blk-cgroup.c | 44 +++++++++++++++++++++++++++++++-------------
1 file changed, 31 insertions(+), 13 deletions(-)

--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1373,13 +1373,14 @@ int blkcg_activate_policy(struct request
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;

+ /* If prealloc matches, use it; otherwise try GFP_NOWAIT */
if (blkg == pinned_blkg) {
pd = pd_prealloc;
pd_prealloc = NULL;
@@ -1389,6 +1390,10 @@ retry:
}

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);
@@ -1396,38 +1401,51 @@ retry:

spin_unlock_irq(&q->queue_lock);

- kfree(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) {
+ if (pd_prealloc)
goto retry;
- } else {
- ret = -ENOMEM;
- goto out_bypass_end;
- }
+ 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);
}

- if (pinned_blkg)
- blkg_put(pinned_blkg);
- kfree(pd_prealloc);
+ /* 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);