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The updating of 'bfqg->ref' should be protected by 'bfqd->lock', however, during code review, we found that bfq_pd_free() update 'bfqg->ref' without holding the lock, which is problematic: 1) bfq_pd_free() triggered by removing cgroup is called asynchronously; 2) bfqq will grab bfqg reference, and exit bfqq will drop the reference, which can concurrent with 1). Unfortunately, 'bfqd->lock' can't be held here because 'bfqd' might already be freed in bfq_pd_free(). Fix the problem by using atomic refcount apis. Signed-off-by: Yu Kuai <yukuai3@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20230103084755.1256479-1-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.