On 12/13/22 14:29, Tejun Heo wrote:
On Tue, Dec 13, 2022 at 01:44:45PM -0500, Waiman Long wrote:Commit 59b57717fff8 ("blkcg: delay blkg destruction until after writeback has finished") delayed call to blkcg_destroy_blkgs() to cgwb_release_workfn(). However, it is done after a css_put() of blkcg which may be the final put that causes the blkcg to be freed as RCU read lock isn't held. Another place where blkcg_destroy_blkgs() can be called indirectly via blkcg_unpin_online() is from the offline_css() function called from css_killed_work_fn(). Over there, the potentially final css_put() call is issued after offline_css(). By adding a css_tryget() into blkcg_destroy_blkgs() and warning its failure, the following stack trace was produced in a test system on bootup.This doesn't agree with the code anymore. Otherwise Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Sorry, I overlooked the commit log in my update. I will update it if I need another version, or Jens can make the following edit:
css_tryget() -> percpu_ref_is_zero(). Thanks, Longman
