Re: [PATCH] blkcg: add rcu lock to bio_clone_blkg_association()

From: Jens Axboe
Date: Fri Dec 21 2018 - 12:03:15 EST

On 12/21/18 10:02 AM, Dennis Zhou wrote:
> On Fri, Dec 21, 2018 at 08:26:02AM -0700, Jens Axboe wrote:
>> On 12/21/18 7:54 AM, Dennis Zhou wrote:
>>> I cleaned up blkg_tryget_closest() to require rcu_read_lock() earlier.
>>> However, this was a subtle case too which clearly was too subtle for me.
>>> The idea was the src bio should be holding a ref to the blkg so rcu
>>> wasn't technically needed. If it doesn't hold a ref, it should be %NULL
>>> and the blkg->parent pointers are unused.
>>> This adds the appropriate read lock in bio_clone_blkg_association().
>> Shall I just fold this with the previous? I staged it in a
>> later-in-merge-cycle branch, so that's not an issue to amend.
> Yeah that would be great!


Jens Axboe