On Wed, Mar 14, 2018 at 12:45:10PM -0700, Tejun Heo wrote: > rvt_mregion uses percpu_ref for reference counting and RCU to protect > accesses from lkey_table. When a rvt_mregion needs to be freed, it > first gets unregistered from lkey_table and then rvt_check_refs() is > called to wait for in-flight usages before the rvt_mregion is freed. > > rvt_check_refs() seems to have a couple issues. > > * It has a fast exit path which tests percpu_ref_is_zero(). However, > a percpu_ref reading zero doesn't mean that the object can be > released. In fact, the ->release() callback might not even have > started executing yet. Proceeding with freeing can lead to > use-after-free. > > * lkey_table is RCU protected but there is no RCU grace period in the > free path. percpu_ref uses RCU internally but it's sched-RCU whose > grace periods are different from regular RCU. Also, it generally > isn't a good idea to depend on internal behaviors like this. > > To address the above issues, this patch removes the fast exit and adds > an explicit synchronize_rcu(). > > Signed-off-by: Tejun Heo <t...@kernel.org> > Acked-by: Dennis Dalessandro <dennis.dalessan...@intel.com> > Cc: Mike Marciniszyn <mike.marcinis...@intel.com> > Cc: linux-r...@vger.kernel.org > Cc: Linus Torvalds <torva...@linux-foundation.org> > drivers/infiniband/sw/rdmavt/mr.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-)
Applied to rdma for-next Thanks, Jason
