path: root/drivers
diff options
authorTejun Heo <tj@kernel.org>2018-03-14 12:45:10 -0700
committerJason Gunthorpe <jgg@mellanox.com>2018-03-15 15:38:19 -0600
commit95da6e96f1e74e6ddfb347f7a8310f419bb47bf7 (patch)
treeb177c6ac11105639dc26f2c2d50170b04f4d8681 /drivers
parentRDMA/qedr: eliminate duplicate barriers on weakly-ordered archs (diff)
RDMAVT: Fix synchronization around percpu_ref
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 <tj@kernel.org> Acked-by: Dennis Dalessandro <dennis.dalessandro@intel.com> Cc: Mike Marciniszyn <mike.marciniszyn@intel.com> Cc: linux-rdma@vger.kernel.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Diffstat (limited to 'drivers')
1 files changed, 6 insertions, 4 deletions
diff --git a/drivers/infiniband/sw/rdmavt/mr.c b/drivers/infiniband/sw/rdmavt/mr.c
index 1b2e5362a3ff..cc429b567d0a 100644
--- a/drivers/infiniband/sw/rdmavt/mr.c
+++ b/drivers/infiniband/sw/rdmavt/mr.c
@@ -489,11 +489,13 @@ static int rvt_check_refs(struct rvt_mregion *mr, const char *t)
unsigned long timeout;
struct rvt_dev_info *rdi = ib_to_rvt(mr->pd->device);
- if (percpu_ref_is_zero(&mr->refcount))
- return 0;
- /* avoid dma mr */
- if (mr->lkey)
+ if (mr->lkey) {
+ /* avoid dma mr */
+ /* @mr was indexed on rcu protected @lkey_table */
+ synchronize_rcu();
+ }
timeout = wait_for_completion_timeout(&mr->comp, 5 * HZ);
if (!timeout) {