linux-kernel - Re: [PATCH block/for-linus] blkcg: Fix multiple bugs in blkcg_activate

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Date:   Tue, 15 Oct 2019 10:13:38 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Tejun Heo <tj@...nel.org>
Cc:     Julia Lawall <julia.lawall@...6.fr>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        linux-block@...r.kernel.org
Subject: Re: [PATCH block/for-linus] blkcg: Fix multiple bugs in
 blkcg_activate_policy()

On 10/15/19 10:03 AM, Tejun Heo wrote:
> 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.

Great thanks, applied.

-- 
Jens Axboe