On 12/19/18 9:13 AM, Mike Snitzer wrote: > On Wed, Dec 19 2018 at 11:11am -0500, > Mike Snitzer <[email protected]> wrote: > >> On Wed, Dec 19 2018 at 10:50am -0500, >> Jens Axboe <[email protected]> wrote: >> >>> DM currently has a statically allocated bio that it uses to issue empty >>> flushes. It doesn't submit this bio, it just uses it for maintaining >>> state while setting up clones. Multiple users can access this bio at the >>> same time. This wasn't previously an issue, even if it was a bit iffy, >>> but with the blkg associations it can become one. >>> >>> We setup the blkg association, then clone bio's and submit, then remove >>> the blkg assocation again. But since we can have multiple tasks doing >>> this at the same time, against multiple blkg's, then we can either lose >>> references to a blkg, or put it twice. The latter causes complaints on >>> the percpu ref being <= 0 when released, and can cause use-after-free as >>> well. Ming reports that xfstest generic/475 triggers this: >>> >>> ------------[ cut here ]------------ >>> percpu ref (blkg_release) <= 0 (0) after switching to atomic >>> WARNING: CPU: 13 PID: 0 at lib/percpu-refcount.c:155 >>> percpu_ref_switch_to_atomic_rcu+0x2c9/0x4a0 >>> >>> Switch to just using an on-stack bio for this, and get rid of the >>> embedded bio. >>> >>> Fixes: 5cdf2e3fea5e ("blkcg: associate blkg when associating a device") >>> Reported-by: Ming Lei <[email protected]> >>> Signed-off-by: Jens Axboe <[email protected]> >> >> Thanks for sorting this one out, definitely wasn't happy with how >> exposed DM was left with the recent blkg changes. This is clearly >> better. >> >> Acked-by: Mike Snitzer <[email protected]> > > Please upgrade this to: > > Reviewed-by: Mike Snitzer <[email protected]>
Done, thanks Mike. -- Jens Axboe
