mm/hmm.c: remove superfluous 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
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>

diff --git a/mm/hmm.c b/mm/hmm.c
index 398d0214be6647534cc9a00cc85df988076327d5..486dc394a5a3cd1fe226e215717631619c8a4195 100644 (file)
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -1024,13 +1024,6 @@ 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;
@@ -1071,9 +1064,8 @@ 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));