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Subject[PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup
Date
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
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