Re: [PATCH 2/6] uprobes: introduce is_swbp_at_addr_fast()

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On Mon, 2012-04-16 at 17:34 +0200, Oleg Nesterov wrote:
> On 04/16, Peter Zijlstra wrote:
> >
> > Can't we 'optimize' read_opcode() by doing the pagefault_disable() +
> > __copy_from_user_inatomic() optimistically before going down the whole
> > gup()+lock+kmap path?
> 
> Unlikely, the task is not current.

Easy enough to test that though.. and that should make the regular path
fast enough, no?


---
 kernel/events/uprobes.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 985be4d..7f5d8c5 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -312,6 +312,15 @@ static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_
 	void *vaddr_new;
 	int ret;
 
+	if (mm == current->mm) {
+		pagefault_disable();
+		ret = __copy_from_user_inatomic(opcode, (void __user *)vaddr, 
+						sizeof(*opcode));
+		pagefault_enable();
+		if (!ret)
+			return 0;
+	}
+
 	ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &page, NULL);
 	if (ret <= 0)
 		return ret;

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