IB/umem: Fix possible hang on process exit
If ib_umem_release() is called after ib_uverbs_close() sets context->closing,
then a process can get stuck in a D state, because the code boils down to
if (down_write_trylock(&mm->mmap_sem))
down_write(&mm->mmap_sem);
which is obviously a stupid instant deadlock. Fix the code so that we
only try to take the lock once.
This bug was introduced in commit f7c6a7b5 ("IB/uverbs: Export
ib_umem_get()/ib_umem_release() to modules") which fortunately never
made it into a release, and was reported by Pete Wyckoff <pw@osc.edu>.
Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index b4aec51..d40652a 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -225,13 +225,15 @@
* up here and not be able to take the mmap_sem. In that case
* we defer the vm_locked accounting to the system workqueue.
*/
- if (context->closing && !down_write_trylock(&mm->mmap_sem)) {
- INIT_WORK(&umem->work, ib_umem_account);
- umem->mm = mm;
- umem->diff = diff;
+ if (context->closing) {
+ if (!down_write_trylock(&mm->mmap_sem)) {
+ INIT_WORK(&umem->work, ib_umem_account);
+ umem->mm = mm;
+ umem->diff = diff;
- schedule_work(&umem->work);
- return;
+ schedule_work(&umem->work);
+ return;
+ }
} else
down_write(&mm->mmap_sem);
