On Thu, Dec 10, 2015 at 11:09:21AM -0800, Andy Lutomirski wrote: > On Thu, Dec 10, 2015 at 10:55 AM, Thomas Gleixner <[email protected]> wrote: > > Jeff, > > > > On Thu, 10 Dec 2015, Jeff Merkey wrote: > > > >> If an int1 hardware breakpoint exception is triggered, but no perf bp > >> pevent block was registered from arch_install_hw_breakpoint, the > >> system will hard hang with the CPU stuck constantly re-interrupting at > >> the same execution address because the resume flag never gets set, and > >> the NOTIFY_DONE state prevents other int1 handlers, including the > >> default handler in do_debug, from running to handle the condition. > >> Can be reproduced by writing a program that sets an execute breakpoint > >> at schedule() without calling arch_install_hw_breakpoint. > >> > >> The proposed fix checks the dr7 register and sets the resume flag in > >> pt->regs if it determines an executed breakpoint was triggered just in > >> case the check lower down fails. I have seen this bug and its a bug. > > > >> Signed-off-by: [email protected] > >> diff --git a/arch/x86/kernel/hw_breakpoint.c > >> b/arch/x86/kernel/hw_breakpoint.c > >> index 50a3fad..6effcae 100644 > >> --- a/arch/x86/kernel/hw_breakpoint.c > >> +++ b/arch/x86/kernel/hw_breakpoint.c > >> @@ -475,6 +475,14 @@ static int hw_breakpoint_handler(struct die_args > >> *args) > >> for (i = 0; i < HBP_NUM; ++i) { > >> if (likely(!(dr6 & (DR_TRAP0 << i)))) > >> continue; > >> + /* > >> + * Set up resume flag to avoid breakpoint recursion when > >> + * returning back to origin in the event an int1 > >> + * exception is triggered and no event handler > >> + * is present. > >> + */ > >> + if ((dr7 & (3 << ((i * 4) + 16))) == 0) > > > > We have proper defines for all of this. See __encode_dr7(). > > > >> + args->regs->flags |= X86_EFLAGS_RF; > > > > If there is a break point installed, then we do the same thing after > > calling perf_bp_event() again. > > On brief inspection, this smells like a microcode bug. Can you send > /proc/cpuinfo output? > > For example, this CPU and microcode combination is known bad: > > processor : 7 > vendor_id : AuthenticAMD > cpu family : 21 > model : 2 > model name : AMD Opteron(tm) Processor 3380 > stepping : 0 > microcode : 0x6000832 > > If this is the issue, I'm not sure we want to be in the business of > working around localized microcode bugs and, if we do, then I think we > should explicitly detect the bug and log about it.
seems like the issue we hit some time ago: http://marc.info/?l=linux-kernel&m=143976421117070&w=2 jirka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
