On 12/16/15, Jeff Merkey <linux....@gmail.com> wrote: > On 12/16/15, Andy Lutomirski <l...@amacapital.net> wrote: >> On Dec 16, 2015 3:12 PM, "Jeff Merkey" <linux....@gmail.com> wrote: >>> >>> Setting a hardware breakpoint at the >>> >>> rex64 sysret >>> >>> instruction at the end of int_ret_from_sys_call causes the system to >>> triple fault >>> and reboot when the breakpoint is triggered. Appears to be related >>> the same problem >>> as the lockup. >>> >>> This function can be stepped over and traced through with the TRAP >>> FLAG set so long as a hardware breakpoint is set somewhere in the >>> function. Otherwise upon exist the system hard hangs. If you break >>> exactly on that instruction -- reboot. If you break a few >>> instructions before it and single step through the call it works. If >>> you step through the call with no breakpoint the system hard hangs. >>> Same behavior as when you try to step from inside an nmi handler. >>> Looks related. >> >> You're probably encountering the user mode RSP when SYSRET happens. >> >> --Andy >> > > Hi Andy, > > Could be, but I am getting a double fault message with an error code > of 0 that then scrolls off the screen when the triple fault hits. It > flashes too quickly to get the function address -- wish I had a logic > analyzer with an inverse assembler -- would already be there. A > usermode RSP would I assume clear TRAP flag and that does not explain > why it works if I set a breakpoint right above the instruction then > step over it, which I can without the triple fault. > > Easy to reproduce, download the mdb debugger for 4.3.3 and apply it to > 4.4-rc5, modprobe mdb, echo a > /proc/sysrq_trigger,
u int_ret_from_sys_call correction sorry (scroll til you get to the swapgs then rex64 > sysret, set a hardware breakpoint at that address , i.e. b > ffffffff81673ae1 (or whatever address the swapgs instruction is at), > then step through with t a few times (should just return after rex64 > sysret since it returns to user space). The set a breakpoint at the > rex64 sysret instruction, b <address>, let it break at the > instruction, then hit g for go and watch the fireworks -- it will try > to print a double fault message then reboot. > > I handle the whole user RSP thing, I just return if I see regs set to > user space. This looks like some sort of problem in the exception > handlers. > > Jeff > -- 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/
