| Date | Fri, 31 Aug 2018 17:26:03 -0700 | From | Tejun Heo <> | Subject | Re: [PATCH 11/15] blkcg: remove additional reference to the css |
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Hello,
On Thu, Aug 30, 2018 at 09:53:52PM -0400, Dennis Zhou wrote: > - css = cgroup_get_e_css(page->mem_cgroup->css.cgroup, &io_cgrp_subsys); > > - return __bio_associate_blkg_from_css(bio, css); > + rcu_read_lock(); > + > + while (true) { > + css = cgroup_e_css(page->mem_cgroup->css.cgroup, > + &io_cgrp_subsys);
So, while they seem similar cgroup_e_css() and cgroup_get_e_css() behave very differently in terms of locking. cgroup_e_css() can only be used under cgroup_mutex because it is used during migration and has to test cgroup_ss_mask(). The right thing to do here would be renaming cgroup_e_css() to something else and add a new implementation which operates in the same way as cgroup_get_e_css().
BTW, this should have triggered lockdep warning. I'd strongly recommend testing with lockdep enabled.
Other than that, looks good to me.
Thanks.
-- tejun
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