On Thu, May 14, 2015 at 09:01:03AM +0900, Masami Hiramatsu wrote: > On 2015/05/14 0:41, William Cohen wrote: > > On 05/13/2015 05:22 AM, Masami Hiramatsu wrote: > >> On 2015/05/12 21:48, William Cohen wrote: > > > >>> Hi Dave, > >>> > >>> In some of the previous diagnostic output it looked like things would go > >>> wrong > >>> in the entry.S when the D bit was cleared and the debug interrupts were > >>> unmasksed. I wonder if some of the issue might be due to the starting > >>> the > >>> kprobe for the trampoline, but leaving things in an odd state when another > >>> set of krpobe/kretporbes are hit when the trampoline is running. > >> > >> Hmm, does this mean we have a trouble if a user kprobe handler calls the > >> function which is probed by other kprobe? Or, is this just a problem > >> only for kretprobes? > > > > Hi Masami, > > > > I wrote an example based off of sample/kprobes/kprobes_sample.c to force > > the reentry issue for kprobes (the attached kprobe_rentry_example.c). That > > seemed to run fine. I think the reason that the trampoline handler got > > into trouble is because of the reset_current_kprobe() before the possible > > call to kfree, but I haven't verified it. > > I still doubt about kfree() reentrant call, since kretprobe handler only > calls recycle_rp_inst() which doesn't free the instance but just push it back > to the unused instance list. > > > It seems like that should be at the end of trampoline handler just before > > the return. Other architectures have similar trampoline handlers, > > so I am surprised that the other architectures haven't encountered this > > issue with kretprobes. Maybe this is due to specific of arm64 exception > > handling. > > Ah, indeed the reset_current_kprobe() here seems not good since some > interruption or some other reason, another kprobes can be hit before > returning. > > If kprobes can handle reentered probes correctly, I think your patch > (directly branch from trampoline) looks good to fix this problem. > Actually, arm32 and x86 already has same method. > > It seems that powerpc will have similar issue, does someone checked > that? Ananth?
Yes, there is a window where this can happen on powerpc. I haven't however been able to trigger it thus far -- will try with a different sample and test. Thanks for the heads-up. Ananth -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/