This is a note to let you know that I've just added the patch titled
RDMAVT: Fix synchronization around percpu_ref
to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: rdmavt-fix-synchronization-around-percpu_ref.patch and it can be found in the queue-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From 74b44bbe80b4c62113ac1501482ea1ee40eb9d67 Mon Sep 17 00:00:00 2001
From: Tejun Heo tj@kernel.org Date: Wed, 14 Mar 2018 12:10:18 -0700 Subject: RDMAVT: Fix synchronization around percpu_ref
From: Tejun Heo tj@kernel.org
commit 74b44bbe80b4c62113ac1501482ea1ee40eb9d67 upstream.
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: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/infiniband/sw/rdmavt/mr.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- 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_mre 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 */ rvt_dereg_clean_qps(mr); + /* @mr was indexed on rcu protected @lkey_table */ + synchronize_rcu(); + } + timeout = wait_for_completion_timeout(&mr->comp, 5 * HZ); if (!timeout) { rvt_pr_err(rdi,
Patches currently in stable-queue which might be from tj@kernel.org are
queue-4.15/rdmavt-fix-synchronization-around-percpu_ref.patch queue-4.15/fs-aio-add-explicit-rcu-grace-period-when-freeing-kioctx.patch queue-4.15/fs-aio-use-rcu-accessors-for-kioctx_table-table.patch