Messages in this thread | | | Date | Wed, 27 Nov 2013 19:55:46 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH/RFC 17/17] tracing/uprobes: Add @+file_offset fetch method |
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Hi Namhyung,
I'll certainly try to read (and even apply ;) this series carefully.
But let me make a couple of nits right now, even if I do not understand this code yet.
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.
> 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.
Oleg.
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