diff options
authorTejun Heo <>2018-03-14 12:10:18 -0700
committerTejun Heo <>2018-03-14 12:10:18 -0700
commit74b44bbe80b4c62113ac1501482ea1ee40eb9d67 (patch)
parentd0264c01e7587001a8c4608a5d1818dba9a4c11a (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 <> Acked-by: Dennis Dalessandro <> Cc: Mike Marciniszyn <> Cc: Cc: Linus Torvalds <>
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) {