From: Tejun Heo <tj@kernel.org>
Date: Tue, 10 Apr 2018 16:29:09 -0700
Subject: mm/hmm.c: remove superfluous RCU protection around radix tree lookup
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Git-commit: 18be460eeb2cd3f4bfb6498b10ce5b800f9a20ea
Patch-mainline: v4.17-rc1
References: HMM fixes, fate#325923, bsc#1104965
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
superfluous 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.
Link: http://lkml.kernel.org/r/20180314194515.1661824-4-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/hmm.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -1024,13 +1024,6 @@ static void hmm_devmem_release(struct de
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;
@@ -1071,9 +1064,8 @@ static int hmm_devmem_pages_create(struc
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));