From: Tejun Heo <tj@xxxxxxxxxx> Subject: 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@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 @@ -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)); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
