Messages in this thread | | | Date | Tue, 17 Apr 2012 19:09:58 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/6] uprobes: introduce is_swbp_at_addr_fast() |
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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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