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    SubjectRe: [PATCH 2/6] uprobes: introduce is_swbp_at_addr_fast()
    On 04/17, Peter Zijlstra wrote:
    >
    > 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;
    > + }

    Indeed. And then we do not need is_swbp_at_addr_fast().

    This reminds me. Why read_opcode() does lock_page? I was going
    to send the cleanup which removes it, but I need to recheck.

    Perhaps you can explain the reason?

    Oleg.



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