From: Tejun Heo <tj@kernel.org>
To: torvalds@linux-foundation.org, jannh@google.com,
paulmck@linux.vnet.ibm.com, bcrl@kvack.org,
viro@zeniv.linux.org.uk, kent.overstreet@gmail.com
Cc: security@kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, Tejun Heo <tj@kernel.org>,
linux-mm@kvack.org
Subject: [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup
Date: Wed, 14 Mar 2018 12:45:11 -0700 [thread overview]
Message-ID: <20180314194515.1661824-4-tj@kernel.org> (raw)
In-Reply-To: <20180314194515.1661824-1-tj@kernel.org>
hmm_devmem_find() requires rcu_read_lock_held() but there's nothing
which actually uses the RCU protection. The only caller is
hmm_devmem_pages_create() which already grabs the mutex and does
superflous rcu_read_lock/unlock() around the function.
This doesn't add anything and just adds to confusion. Remove the RCU
protection and open-code the radix tree lookup. If this needs to
become more sophisticated in the future, let's add them back when
necessary.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Cc: linux-mm@kvack.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
---
Hello,
Jérôme, how do you want to route this patch? If you prefer, I can
route it together with other patches.
Thanks.
mm/hmm.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)
diff --git a/mm/hmm.c b/mm/hmm.c
index 320545b98..d4627c5 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -845,13 +845,6 @@ static void hmm_devmem_release(struct device *dev, void *data)
hmm_devmem_radix_release(resource);
}
-static struct hmm_devmem *hmm_devmem_find(resource_size_t phys)
-{
- WARN_ON_ONCE(!rcu_read_lock_held());
-
- return radix_tree_lookup(&hmm_devmem_radix, phys >> PA_SECTION_SHIFT);
-}
-
static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
{
resource_size_t key, align_start, align_size, align_end;
@@ -892,9 +885,8 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) {
struct hmm_devmem *dup;
- rcu_read_lock();
- dup = hmm_devmem_find(key);
- rcu_read_unlock();
+ dup = radix_tree_lookup(&hmm_devmem_radix,
+ key >> PA_SECTION_SHIFT);
if (dup) {
dev_err(device, "%s: collides with mapping for %s\n",
__func__, dev_name(dup->device));
--
2.9.5
next prev parent reply other threads:[~2018-03-14 19:45 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-14 19:41 [PATCHSET v2] percpu_ref, RCU: Audit RCU usages in percpu_ref users Tejun Heo
2018-03-14 19:45 ` [PATCH 1/8] fs/aio: Add explicit RCU grace period when freeing kioctx Tejun Heo
2018-03-14 19:45 ` [PATCH 2/8] fs/aio: Use RCU accessors for kioctx_table->table[] Tejun Heo
2018-03-14 19:45 ` [PATCH 3/8] RDMAVT: Fix synchronization around percpu_ref Tejun Heo
2018-03-15 22:24 ` Jason Gunthorpe
2018-03-14 19:45 ` Tejun Heo [this message]
2018-03-26 14:54 ` [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup Tejun Heo
2018-03-27 16:12 ` Jerome Glisse
2018-03-14 19:45 ` [PATCH 5/8] percpu_ref: Update doc to dissuade users from depending on internal RCU grace periods Tejun Heo
2018-03-19 17:10 ` Tejun Heo
2018-03-14 19:45 ` [PATCH 6/8] RCU, workqueue: Implement rcu_work Tejun Heo
2018-03-14 20:13 ` Paul E. McKenney
2018-03-16 6:01 ` Lai Jiangshan
2018-03-19 16:45 ` Tejun Heo
2018-03-20 10:04 ` Lai Jiangshan
2018-03-14 19:45 ` [PATCH 7/8] cgroup: Use rcu_work instead of explicit rcu and work item Tejun Heo
2018-03-14 19:45 ` [PATCH 8/8] fs/aio: " Tejun Heo
2018-03-19 17:12 ` Tejun Heo
2018-03-21 15:58 ` Oleg Nesterov
2018-03-21 16:40 ` Tejun Heo
2018-03-21 17:17 ` Oleg Nesterov
2018-03-21 17:53 ` Tejun Heo
2018-03-22 11:24 ` Oleg Nesterov
2018-03-26 15:04 ` Tejun Heo
2018-03-27 14:28 ` Oleg Nesterov
2018-03-27 15:55 ` Tejun Heo
2018-03-29 16:49 ` Oleg Nesterov
2018-03-29 17:41 ` Tejun Heo
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