On 2013/8/23 0:42, Steven Rostedt wrote: > On Fri, 09 Aug 2013 18:56:54 +0900 > Masami Hiramatsu <masami.hiramatsu...@hitachi.com> wrote: > >> (2013/08/09 17:45), Namhyung Kim wrote: >>> From: Namhyung Kim <namhyung....@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 > I also thought out this approach, but the issue is we cannot fetch user memory into per-cpu buffer, because use per-cpu buffer should under preempt disabled, and fetching user memory could sleep.
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