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[80.7.220.175]) by smtp.gmail.com with ESMTPSA id z19sm3725087wmk.12.2020.11.02.01.19.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2020 01:19:03 -0800 (PST) Date: Mon, 2 Nov 2020 09:19:01 +0000 From: Daniel Thompson To: Sumit Garg Cc: Marc Zyngier , Catalin Marinas , Will Deacon , linux-arm-kernel , Thomas Gleixner , Jason Cooper , Russell King - ARM Linux admin , tsbogend@alpha.franken.de, mpe@ellerman.id.au, "David S. Miller" , mingo@redhat.com, bp@alien8.de, x86@kernel.org, Mark Rutland , julien.thierry.kdev@gmail.com, Douglas Anderson , Jason Wessel , Masayoshi Mizuma , ito-yuichi@fujitsu.com, kgdb-bugreport@lists.sourceforge.net, Linux Kernel Mailing List Subject: Re: [PATCH v6 6/7] kgdb: roundup: Allow runtime arch specific override Message-ID: <20201102091901.fkxdp2wyiycdhtjm@holly.lan> References: <1603983387-8738-1-git-send-email-sumit.garg@linaro.org> <1603983387-8738-7-git-send-email-sumit.garg@linaro.org> <20201029152106.gj66mjnathsdqtoe@holly.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 02, 2020 at 11:48:53AM +0530, Sumit Garg wrote: > On Thu, 29 Oct 2020 at 20:51, Daniel Thompson > wrote: > > > > On Thu, Oct 29, 2020 at 08:26:26PM +0530, Sumit Garg wrote: > > > Add a new API kgdb_arch_roundup_cpus() for a particular archichecture to > > > override default kgdb roundup and if it detects at runtime to not support > > > NMI roundup then it can fallback to default implementation using async > > > SMP cross-calls. > > > > > > Currently such an architecture example is arm64 supporting pseudo NMIs > > > feature which is only available on platforms which have support for GICv3 > > > or later version. > > > > > > Signed-off-by: Sumit Garg > > > --- > > > arch/powerpc/kernel/kgdb.c | 3 ++- > > > arch/sparc/kernel/smp_64.c | 3 ++- > > > arch/x86/kernel/kgdb.c | 6 ++++-- > > > include/linux/kgdb.h | 5 +++-- > > > kernel/debug/debug_core.c | 10 +++++++++- > > > 5 files changed, 20 insertions(+), 7 deletions(-) > > > > > > diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c > > > index 4090802..126575d 100644 > > > --- a/arch/powerpc/kernel/kgdb.c > > > +++ b/arch/powerpc/kernel/kgdb.c > > > @@ -125,9 +125,10 @@ static int kgdb_debugger_ipi(struct pt_regs *regs) > > > } > > > > > > #ifdef CONFIG_SMP > > > -void kgdb_roundup_cpus(void) > > > +bool kgdb_arch_roundup_cpus(void) > > > { > > > smp_send_debugger_break(); > > > + return true; > > > } > > > #endif > > > > > > diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c > > > index e38d8bf..c459c83 100644 > > > --- a/arch/sparc/kernel/smp_64.c > > > +++ b/arch/sparc/kernel/smp_64.c > > > @@ -1014,9 +1014,10 @@ void flush_dcache_page_all(struct mm_struct *mm, struct page *page) > > > } > > > > > > #ifdef CONFIG_KGDB > > > -void kgdb_roundup_cpus(void) > > > +bool kgdb_arch_roundup_cpus(void) > > > { > > > smp_cross_call(&xcall_kgdb_capture, 0, 0, 0); > > > + return true; > > > } > > > #endif > > > > > > diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c > > > index ff7878d..1b756d9 100644 > > > --- a/arch/x86/kernel/kgdb.c > > > +++ b/arch/x86/kernel/kgdb.c > > > @@ -404,7 +404,8 @@ static void kgdb_disable_hw_debug(struct pt_regs *regs) > > > > > > #ifdef CONFIG_SMP > > > /** > > > - * kgdb_roundup_cpus - Get other CPUs into a holding pattern > > > + * kgdb_arch_roundup_cpus - Get other CPUs into a holding pattern > > > + * in an architectural specific manner > > > * > > > * On SMP systems, we need to get the attention of the other CPUs > > > * and get them be in a known state. This should do what is needed > > > @@ -414,9 +415,10 @@ static void kgdb_disable_hw_debug(struct pt_regs *regs) > > > * > > > * On non-SMP systems, this is not called. > > > */ > > > -void kgdb_roundup_cpus(void) > > > +bool kgdb_arch_roundup_cpus(void) > > > { > > > apic_send_IPI_allbutself(NMI_VECTOR); > > > + return true; > > > } > > > #endif > > > > > > diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h > > > index 0d6cf64..f9db5b8 100644 > > > --- a/include/linux/kgdb.h > > > +++ b/include/linux/kgdb.h > > > @@ -200,7 +200,8 @@ kgdb_arch_handle_qxfer_pkt(char *remcom_in_buffer, > > > extern void kgdb_call_nmi_hook(void *ignored); > > > > > > /** > > > - * kgdb_roundup_cpus - Get other CPUs into a holding pattern > > > + * kgdb_arch_roundup_cpus - Get other CPUs into a holding pattern > > > + * in an architectural specific manner > > > * > > > * On SMP systems, we need to get the attention of the other CPUs > > > * and get them into a known state. This should do what is needed > > > @@ -210,7 +211,7 @@ extern void kgdb_call_nmi_hook(void *ignored); > > > * > > > * On non-SMP systems, this is not called. > > > */ > > > -extern void kgdb_roundup_cpus(void); > > > +extern bool kgdb_arch_roundup_cpus(void); > > > > > > /** > > > * kgdb_arch_set_pc - Generic call back to the program counter > > > diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c > > > index 1e75a89..27e401c 100644 > > > --- a/kernel/debug/debug_core.c > > > +++ b/kernel/debug/debug_core.c > > > @@ -241,13 +241,21 @@ void __weak kgdb_call_nmi_hook(void *ignored) > > > } > > > NOKPROBE_SYMBOL(kgdb_call_nmi_hook); > > > > > > -void __weak kgdb_roundup_cpus(void) > > > +bool __weak kgdb_arch_roundup_cpus(void) > > > +{ > > > + return false; > > > > Do we really need to introduce all these boolean return values just to > > call a bit of library code when one of the architectures wants to > > fallback to a generic implementation? > > > > Why not something more like: > > > > void kgdb_smp_call_nmi_hook(void) > > { > > /* original weak version of kgdb_roundup_cpus goes here */ > > } > > > > void __weak kgdb_roundup_cpus(void) > > { > > kgdb_smp_call_nmi_hook(); > > } > > > > arm64 can now simply call the new library function if a fallback is needed. > > > > Makes sense, I will use this approach instead. > > > Note that same question applies to the backtrace changes... > > In case of backtrace, there are already multiple APIs wrapping > arch_trigger_cpumask_backtrace() as follows: > > - trigger_all_cpu_backtrace() > - trigger_allbutself_cpu_backtrace() > - trigger_cpumask_backtrace() > - trigger_single_cpu_backtrace() > > And each of them already return a boolean and have corresponding > different fallback mechanisms. So we can't have a common fallback API > from arch specific code and instead need to extend that boolean return > to arch specific code that is implemented as part of patch #4. Understood. Thanks. Daniel.