Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754556AbaK0JuL (ORCPT ); Thu, 27 Nov 2014 04:50:11 -0500 Received: from mail-wi0-f171.google.com ([209.85.212.171]:46896 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751512AbaK0JuH (ORCPT ); Thu, 27 Nov 2014 04:50:07 -0500 Message-ID: <5476F3C5.8020709@linaro.org> Date: Thu, 27 Nov 2014 09:49:57 +0000 From: Daniel Thompson User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Colin Cross , Kiran Raparthy CC: lkml , Jason Wessel , kgdb-bugreport@lists.sourceforge.net, Android Kernel Team , John Stultz , Sumit Semwal Subject: Re: [RFC v3] debug: prevent entering debug mode on errors References: <1416993266-16514-1-git-send-email-kiran.kumar@linaro.org> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? -- 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/