Commit 18be460e authored Apr 10, 2018 by Tejun Heo Committed by Linus Torvalds Apr 11, 2018

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>

parent f88a1e90

mm/hmm.c

+2 −10

Original line number	Diff line number	Diff line
		@@ -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));

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