Hi Oleg,
On Wed, 27 Nov 2013 19:55:46 +0100, Oleg Nesterov wrote:
> Hi Namhyung,
>
> I'll certainly try to read (and even apply ;) this series carefully.
Thanks in advance. :)
>
> But let me make a couple of nits right now, even if I do not understand
> this code yet.
Okay.
>
> On 11/27, Namhyung Kim wrote:
>>
>> + } else if (arg[1] == '+') {
>> + struct file_offset_fetch_param *foprm;
>> +
>> + /* kprobes don't support file offsets */
>> + if (is_kprobe)
>> + return -EINVAL;
>> +
>> + ret = kstrtol(arg + 2, 0, &offset);
>> + if (ret)
>> + break;
>> +
>> + foprm = kzalloc(sizeof(*foprm), GFP_KERNEL);
>> + if (!foprm)
>> + return -ENOMEM;
>> +
>> + foprm->tu = priv;
>> + foprm->offset = offset;
>
> Hmm. I am not sure, but can't we simplify this?
>
> Why do we need this foprm at all? To pass tu/offset obviously. But
> why we need to store this info in fetch_param?
>
> translate_user_vaddr() needs to access utask->vaddr anyway. It seems
> to me it would be more clean to do the following:
>
> 1. Add
> struct xxx {
> struct trace_uprobe *tu;
> unsigned long bp_addr;
> };
>
> in trace_uprobe.c.
>
> 2. Add
>
> struct xxx info = {
> .tu = tu,
> .bp_addr = instruction_pointer(regs);
> };
>
> current->utask->vaddr = (long)&info;
>
> into uprobe_dispatcher() and uretprobe_dispatcher() (the latter
> should obviously use func instead of instruction_pointer).
>
> 3. FETCH_FUNC_NAME(file_offset, type) can do
>
> struct xxx *info = (void*)current->utask->vaddr;
> void *addr = data + info->bp_addr - info->tu->offset;
>
> return FETCH_FUNC_NAME(memory, type)(regs, aaddr, dest);
>
> 4. Now, the only change we need in parse_probe_arg("@") is that
> it should use either FETCH_MTD_memory or FETCH_MTD_file_offset
> depending on arg[0] == '+'.
>
> And we do not need to pass "void *prive" to parse_probe_arg().
>
> What do you think? One again, I can be easily wrong, I didn't read the
> code yet.
You are absolutely right.
I thought we need a fetch_param anyway if we will add support for
cross-fetch later. But I won't insist it strongly, I can delay it to
later work and make current code simpler if you want. :)
>
>> static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs
>> *regs)
>> {
>> struct trace_uprobe *tu;
>> + struct uprobe_task *utask;
>> int ret = 0;
>>
>> tu = container_of(con, struct trace_uprobe, consumer);
>> tu->nhit++;
>>
>> + utask = current->utask;
>> + if (utask == NULL)
>> + return UPROBE_HANDLER_REMOVE;
>
> Hmm, why? The previous change ensures ->utask is not NULL? If we hit
> NULL we have a bug, we should not remove this uprobe.
Yes, I just want to be defensive. :)
So do you suggest to add BUG_ON()? And can I convert or remove a
similar check in uprobes.c:pre_ssout() too?
Thanks,
Namhyung
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