On Fri, 2012-04-06 at 00:21 +0200, Oleg Nesterov wrote:
> +int __weak is_swbp_at_addr_fast(unsigned long vaddr)
> +{
> + uprobe_opcode_t opcode;
> + int fault;
> +
> + pagefault_disable();
> + fault = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
> + sizeof(opcode));
> + pagefault_enable();
> +
> + if (unlikely(fault)) {
> + /*
> + * XXX: read_opcode() lacks FOLL_FORCE, it can fail if
> + * we race with another thread which does mprotect(NONE)
> + * after we hit bp.
> + */
> + if (read_opcode(current->mm, vaddr, &opcode))
> + return -EFAULT;
> + }
> +
> + return is_swbp_insn(&opcode);
> +}
Why bother with the pagefault_disable() and unlikely fault case and not
simply do copy_from_user() and have it deal with the fault if its needed
anyway?
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