Messages in this thread | | | Date | Thu, 20 Nov 2014 13:48:09 +0530 | Subject | Re: [RFC] debug: add parameters to prevent entering debug mode on errors | From | Kiran Raparthy <> |
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Hi Daniel,
On 18 November 2014 22:43, Daniel Thompson <daniel.thompson@linaro.org> wrote: > On 18/11/14 12:08, Kiran Kumar Raparthy wrote: >> From: Colin Cross <ccross@android.com> >> >> debug: add parameters to prevent entering debug mode on errors >> >> On non-developer devices kgdb prevents CONFIG_PANIC_TIMEOUT from rebooting the >> device after a panic. Add module parameters debug_core.break_on_exception and >> debug_core.break_on_panic to allow skipping debug on panics and exceptions >> respectively. Both default to true to preserve existing behavior. > > I am a little unsure about break_on_panic. > > It ought to be possible for kgdb/kdb to honour CONFIG_PANIC_TIMEOUT by > tracking how long it takes for the user to attach a debugger (or to run > the first kdb command after the panic). As it happens the timeout value > is already an exported kernel symbol so all the info it there for us to > use... > > Doing so would save us imposing further configuration burden on the user > (although it would be a good deal more code). > > Note that I can't think of an automatic way to handle break_on_exception > so I'm less worried about that one. Alright,so it it okay if we have this mechanism limited to "skip debug on exceptions"? please let me know if i have misunderstood your point. > > >> Cc: Jason Wessel <jason.wessel@windriver.com> >> Cc: kgdb-bugreport@lists.sourceforge.net >> Cc: linux-kernel@vger.kernel.org >> Cc: Android Kernel Team <kernel-team@android.com> >> Cc: John Stultz <john.stultz@linaro.org> >> Cc: Sumit Semwal <sumit.semwal@linaro.org> >> Signed-off-by: Colin Cross <ccross@android.com> >> [Kiran: Added context to commit message] >> Signed-off-by: Kiran Raparthy <kiran.kumar@linaro.org> >> --- >> This is one of the number of patches from the Android AOSP common.git tree, >> which is used on almost all Android devices. I wanted to submit it for review >> to see if it should go upstream. >> >> kernel/debug/debug_core.c | 12 ++++++++++++ >> 1 file changed, 12 insertions(+) >> >> diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c >> index 1adf62b..af06122 100644 >> --- a/kernel/debug/debug_core.c >> +++ b/kernel/debug/debug_core.c >> @@ -87,6 +87,10 @@ static int kgdb_use_con; >> bool dbg_is_early = true; >> /* Next cpu to become the master debug core */ >> int dbg_switch_cpu; >> +/* Flag for entering kdb when a panic occurs */ >> +static bool break_on_panic = true; >> +/* Flag for entering kdb when an exception occurs */ >> +static bool break_on_exception = true; >> >> /* Use kdb or gdbserver mode */ >> int dbg_kdb_mode = 1; >> @@ -101,6 +105,8 @@ early_param("kgdbcon", opt_kgdb_con); >> >> module_param(kgdb_use_con, int, 0644); >> module_param(kgdbreboot, int, 0644); >> +module_param(break_on_panic, bool, 0644); >> +module_param(break_on_exception, bool, 0644); > > kgdbreboot, which controls whether or not to trap into kgdb during > reboot, has a similar purpose to these new parameters. Perhaps any new > symbols should follow a similar naming scheme. > >> /* >> * Holds information about breakpoints in a kernel. These breakpoints are >> @@ -690,6 +696,9 @@ 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); >> >> + if (unlikely(signo != SIGTRAP && !break_on_exception)) > > This is nit picking but... > > There should be no need to predict branch results here. Its not > performance critical and anyway the "fast" path implied by the > unlikely() results in all CPUs screaming to a halt and burning up > millions of cycles waiting for user input. Thanks for your time and review comments. Regards, Kiran > >> + return 1; >> + >> memset(ks, 0, sizeof(struct kgdb_state)); >> ks->cpu = raw_smp_processor_id(); >> ks->ex_vector = evector; >> @@ -821,6 +830,9 @@ static int kgdb_panic_event(struct notifier_block *self, >> unsigned long val, >> void *data) >> { >> + if (!break_on_panic) >> + return NOTIFY_DONE; >> + >> if (dbg_kdb_mode) >> kdb_printf("PANIC: %s\n", (char *)data); >> kgdb_breakpoint(); >> >
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