The patch titled
Subject: mm/hmm.c: remove superflous RCU protection around radix tree lookup
has been added to the -mm tree. Its filename is
hmm-remove-superflous-rcu-protection-around-radix-tree-lookup.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/hmm-remove-superflous-rcu-protection-around-radix-tree-lookup.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/hmm-remove-superflous-rcu-protection-around-radix-tree-lookup.patch
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------------------------------------------------------
From: Tejun Heo <tj@xxxxxxxxxx>
Subject: mm/hmm.c: remove superflous RCU protection around radix tree lookup
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.
Link: http://lkml.kernel.org/r/20180314194515.1661824-4-tj@xxxxxxxxxx
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Benjamin LaHaise <bcrl@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hmm.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)
diff -puN mm/hmm.c~hmm-remove-superflous-rcu-protection-around-radix-tree-lookup mm/hmm.c
--- a/mm/hmm.c~hmm-remove-superflous-rcu-protection-around-radix-tree-lookup
+++ a/mm/hmm.c
@@ -1019,13 +1019,6 @@ 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;
@@ -1066,9 +1059,8 @@ 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));
_
Patches currently in -mm which might be from tj@xxxxxxxxxx are
hmm-remove-superflous-rcu-protection-around-radix-tree-lookup.patch
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