On Wed, 15 Jun 2022 22:00:29 +0200 Dmitry Dolgov <9erthalion6@xxxxxxxxx> wrote: > > On Sun, Jun 12, 2022 at 09:12:32PM +0900, Masami Hiramatsu wrote: > > On Sat, 11 Jun 2022 11:28:36 -0700 > > Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > > > > On Thu, Jun 9, 2022 at 1:14 PM Dmitry Dolgov <9erthalion6@xxxxxxxxx> wrote: > > > > > > > > > On Thu, Jun 09, 2022 at 09:29:36PM +0200, Dmitrii Dolgov wrote: > > > > > > > > > > Enable specifying maxactive for fd based kretprobe. This will be useful > > > > > for tracing tools like bcc and bpftrace (see for example discussion [1]). > > > > > Use highest 12 bit (bit 52-63) to allow maximal maxactive of 4095. > > > > > > > > > > The original patch [2] seems to be fallen through the cracks and wasn't > > > > > applied. I've merely rebased the work done by Song Liu and verififed it > > > > > still works. > > > > > > > > > > [1]: https://github.com/iovisor/bpftrace/issues/835 > > > > > [2]: https://lore.kernel.org/all/20191007223111.1142454-1-songliubraving@xxxxxx/ > > > > > > > > I've recently stumbled upon this seemingly lost topic, and wanted to raise it > > > > again. Please let me know if there is a more appropriate way to do so. > > > > > > With kretprobe using rethook the maxactive limit is no longer used. > > > So we probably don't need this patch. > > > > > > Masami, wdyt? > > > > No, rethook is just a library version of kretprobe return hook, > > so the maxactive is still alive. I would like to make the rethook > > to use(share with) function graph's per-task shadow stack. When > > that is done, the maxactive will be removed. > > Thanks for clarification! Does it mean that the possibility of setting > maxactive still makes sense, until the rethook changes you've mentioned > will land? Yes, unfortunatelly, there is no magic. We need a shadow stack without runtime allocation for this purpose. Thus what we can do is to use a per-task pre-allocated shadow stack page or make a common pool of nodes for variable-length shadow-stack. Both has pros and cons (depends on the system configuration). > > On a side note, is it possible to somehow follow/review/test the work > about rethook and function graph's shadow stack? Hmm, good question. It should work theoletically, but it is easy to be tested by ftrace tracefs interface on x86. Just enable function-graph tracer and add a kretprobe event on some fucntion. E.g. echo function-graph > current_tracer echo r:test vfs_read >> kprobe_events echo 1 > events/kprobes/enable Thank you, -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
