Messages in this thread | | | Date | Mon, 16 Apr 2012 16:44:57 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/6] uprobes: introduce is_swbp_at_addr_fast() |
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On 04/16, Peter Zijlstra wrote: > > 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?
But we can't do this under down_read(mmap_sem) ?
If another thread waits for down_write() then do_page_fault() can't take this lock, right?
Oleg.
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