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SubjectRe: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer
On Fri, 09 Aug 2013 18:56:54 +0900
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:

> (2013/08/09 17:45), Namhyung Kim wrote:
> > From: Namhyung Kim <namhyung.kim@lge.com>
> >
> > Fetching from user space should be done in a non-atomic context. So
> > use a temporary buffer and copy its content to the ring buffer
> > atomically.
> >
> > While at it, use __get_data_size() and store_trace_args() to reduce
> > code duplication.
>
> I just concern using kmalloc() in the event handler. For fetching user
> memory which can be swapped out, that is true. But most of the cases,
> we can presume that it exists on the physical memory.
>


What about creating a per cpu buffer when uprobes are registered, and
delete them when they are finished? Basically what trace_printk() does
if it detects that there are users of trace_printk() in the kernel.
Note, it does not deallocate them when finished, as it is never
finished until reboot ;-)

-- Steve


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