tree 8f048fd73d864a8f41917068d6e610fc5b0e0f0b
parent 838f13bf4b6737d4aec508558e45f81798fc2677
author Tejun Heo <tj@kernel.org> 1436474388 -0400
committer Jens Axboe <axboe@fb.com> 1436474468 -0600

blkcg: blkcg_css_alloc() should grab blkcg_pol_mutex while iterating blkcg_policy[]

An entry in blkcg_policy[] is stable while there are non-bypassing
in-flight IOs on a request_queue which has the policy activated.  This
is why most derefs of blkcg_policy[] don't need explicit locking;
however, blkcg_css_alloc() isn't invoked from IO path and thus doesn't
have this protection and may race policies being added and removed.

Fix it by adding explicit blkcg_pol_mutex protection around
blkcg_policy[] iteration in blkcg_css_alloc().

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: e48453c386f3 ("block, cgroup: implement policy-specific per-blkcg data")
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>