Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752483AbaLAGCp (ORCPT ); Mon, 1 Dec 2014 01:02:45 -0500 Received: from mail-qc0-f182.google.com ([209.85.216.182]:45557 "EHLO mail-qc0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751243AbaLAGCo (ORCPT ); Mon, 1 Dec 2014 01:02:44 -0500 MIME-Version: 1.0 In-Reply-To: <5476F3C5.8020709@linaro.org> References: <1416993266-16514-1-git-send-email-kiran.kumar@linaro.org> <5476F3C5.8020709@linaro.org> Date: Mon, 1 Dec 2014 11:32:43 +0530 Message-ID: Subject: Re: [RFC v3] debug: prevent entering debug mode on errors From: Kiran Raparthy To: Daniel Thompson Cc: Colin Cross , lkml , Jason Wessel , kgdb-bugreport@lists.sourceforge.net, Android Kernel Team , John Stultz , Sumit Semwal Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jason, On 27 November 2014 at 15:19, Daniel Thompson wrote: > On 26/11/14 17:45, Colin Cross wrote: >> On Wed, Nov 26, 2014 at 1:14 AM, Kiran Raparthy wrote: >>> From: Colin Cross >>> >>> debug: prevent entering debug mode on errors >>> >>> On non-developer devices kgdb prevents CONFIG_PANIC_TIMEOUT from rebooting the >>> device after a panic. >>> >>> In case of panics and exceptions, to honor CONFIG_PANIC_TIMEOUT, prevent >>> entering debug mode to avoid getting stuck waiting for the user to interact >>> with debugger. >>> >>> Cc: Jason Wessel >>> Cc: kgdb-bugreport@lists.sourceforge.net >>> Cc: linux-kernel@vger.kernel.org >>> Cc: Android Kernel Team >>> Cc: John Stultz >>> Cc: Sumit Semwal >>> Signed-off-by: Colin Cross >>> [Kiran: Added context to commit message. >>> panic_timeout is used instead of break_on_panic and >>> break_on_exception to honor CONFIG_PANIC_TIMEOUT] >>> Signed-off-by: Kiran Raparthy >>> --- >>> kernel/debug/debug_core.c | 17 +++++++++++++++++ >>> 1 file changed, 17 insertions(+) >>> >>> diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c >>> index 1adf62b..0012a1f 100644 >>> --- a/kernel/debug/debug_core.c >>> +++ b/kernel/debug/debug_core.c >>> @@ -689,6 +689,14 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs) >>> >>> if (arch_kgdb_ops.enable_nmi) >>> arch_kgdb_ops.enable_nmi(0); >>> + /* >>> + * Avoid entering the debugger if we were triggered due to an oops >>> + * but panic_timeout indicates the system should automatically >>> + * reboot on panic. We don't want to get stuck waiting for input >>> + * on such systems, especially if its "just" an oops. >>> + */ >>> + if (signo != SIGTRAP && panic_timeout) >>> + return 1; >>> >>> memset(ks, 0, sizeof(struct kgdb_state)); >>> ks->cpu = raw_smp_processor_id(); >>> @@ -821,6 +829,15 @@ static int kgdb_panic_event(struct notifier_block *self, >>> unsigned long val, >>> void *data) >>> { >>> + /* >>> + * Avoid entering the debugger if we were triggered due to a panic >>> + * We don't want to get stuck waiting for input from user in such case. >>> + * panic_timeout indicates the system should automatically >>> + * reboot on panic. >>> + */ >>> + if (panic_timeout) >>> + return NOTIFY_DONE; >>> + >>> if (dbg_kdb_mode) >>> kdb_printf("PANIC: %s\n", (char *)data); >>> kgdb_breakpoint(); >> >> The original patch was more useful as it allowed re-enabling break on >> panic on specific devices where you were trying to debug a >> reproducible issue. What about using a module_param similar to >> kgdbreboot, but setting the default based on CONFIG_PANIC_TIMEOUT to >> avoid extra configuration? > > This change was due to my review so perhaps I'd better answer this... > > panic_timeout is the value of the panic sysctl. In addition to the > normal sysctl tooling (which I don't think is available on most android > systems), its value can be set using panic=0 on the kernel command line > or via /proc/sys/kernel/panic at runtime. > > CONFIG_PANIC_TIMEOUT merely sets the default value of the sysctl. I > guess perhaps the patch description could be improved to make this clearer. > > Therefore, the only loss of function I expected versus the original is > that it would be hard to get as far as a reproducible panic if the > system also has a ton of reproducible oopses that we don't want to fix. > Is such a use-case important? Could you please let me know if this patch is good to move from RFC to PATCH? Regards, Kiran -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/