[PATCH 1/7] uprobes: optimize is_swbp_at_addr() for current->mm

[Oleg Nesterov <oleg@redhat.com>]

Change is_swbp_at_addr() to try to avoid the costly read_opcode()
if mm == current->mm, __copy_from_user_inatomic() should succeed
in the likely case.

Currently this optimization is not important, but we are going to
add more is_swbp_at_addr(current->mm) callers.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/events/uprobes.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 985be4d..d0f5ec0 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -333,10 +333,20 @@ static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
 	uprobe_opcode_t opcode;
 	int result;
 
+	if (current->mm == mm) {
+		pagefault_disable();
+		result = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
+								sizeof(opcode));
+		pagefault_enable();
+
+		if (likely(result == 0))
+			goto out;
+	}
+
 	result = read_opcode(mm, vaddr, &opcode);
 	if (result)
 		return result;
-
+out:
 	if (is_swbp_insn(&opcode))
 		return 1;
 
-- 
1.5.5.1