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Message-ID: <20240420114207.GG614130@ravnborg.org>
Date: Sat, 20 Apr 2024 13:42:07 +0200
From: Sam Ravnborg <sam@...nborg.org>
To: Dawei Li <dawei.li@...ngroup.cn>
Cc: davem@...emloft.net, andreas@...sler.com, sparclinux@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/7] sparc/smp: Remove on-stack cpumask var
Hi Dawei
On Sat, Apr 20, 2024 at 01:15:47PM +0800, Dawei Li wrote:
> In general it's preferable to avoid placing cpumasks on the stack, as
> for large values of NR_CPUS these can consume significant amounts of
> stack space and make stack overflows more likely.
>
> - Change prototype of sparc32_ipi_ops::cross_call() so that it takes
> const cpumask * arg and all its callers accordingly.
>
> - As for all cross_call() implementations, divide cpumask_test_cpu() call
> into several sub calls to avoid on-stack cpumask var.
>
> Signed-off-by: Dawei Li <dawei.li@...ngroup.cn>
The code changes looks ok from a quick look.
But we have a bunch of patches pending touching or removing the same
files. On top of this, the right approach would be to take a
look at code from a higher level.
In other words - I advise to drop this, and maybe re-visit in a few
months after the pending patches has hit -next.
Sorry for asking you to look as this.
Sam
> ---
> arch/sparc/include/asm/smp_32.h | 12 ++++++------
> arch/sparc/kernel/kernel.h | 11 +++++++++++
> arch/sparc/kernel/leon_smp.c | 11 ++++-------
> arch/sparc/kernel/sun4d_smp.c | 10 ++++------
> arch/sparc/kernel/sun4m_smp.c | 10 ++++------
> 5 files changed, 29 insertions(+), 25 deletions(-)
>
> diff --git a/arch/sparc/include/asm/smp_32.h b/arch/sparc/include/asm/smp_32.h
> index 2cf7971d7f6c..9b6a166f6a57 100644
> --- a/arch/sparc/include/asm/smp_32.h
> +++ b/arch/sparc/include/asm/smp_32.h
> @@ -54,7 +54,7 @@ void smp_bogo(struct seq_file *);
> void smp_info(struct seq_file *);
>
> struct sparc32_ipi_ops {
> - void (*cross_call)(void *func, cpumask_t mask, unsigned long arg1,
> + void (*cross_call)(void *func, const cpumask_t *mask, unsigned long arg1,
> unsigned long arg2, unsigned long arg3,
> unsigned long arg4);
> void (*resched)(int cpu);
> @@ -65,29 +65,29 @@ extern const struct sparc32_ipi_ops *sparc32_ipi_ops;
>
> static inline void xc0(void *func)
> {
> - sparc32_ipi_ops->cross_call(func, *cpu_online_mask, 0, 0, 0, 0);
> + sparc32_ipi_ops->cross_call(func, cpu_online_mask, 0, 0, 0, 0);
> }
>
> static inline void xc1(void *func, unsigned long arg1)
> {
> - sparc32_ipi_ops->cross_call(func, *cpu_online_mask, arg1, 0, 0, 0);
> + sparc32_ipi_ops->cross_call(func, cpu_online_mask, arg1, 0, 0, 0);
> }
> static inline void xc2(void *func, unsigned long arg1, unsigned long arg2)
> {
> - sparc32_ipi_ops->cross_call(func, *cpu_online_mask, arg1, arg2, 0, 0);
> + sparc32_ipi_ops->cross_call(func, cpu_online_mask, arg1, arg2, 0, 0);
> }
>
> static inline void xc3(void *func, unsigned long arg1, unsigned long arg2,
> unsigned long arg3)
> {
> - sparc32_ipi_ops->cross_call(func, *cpu_online_mask,
> + sparc32_ipi_ops->cross_call(func, cpu_online_mask,
> arg1, arg2, arg3, 0);
> }
>
> static inline void xc4(void *func, unsigned long arg1, unsigned long arg2,
> unsigned long arg3, unsigned long arg4)
> {
> - sparc32_ipi_ops->cross_call(func, *cpu_online_mask,
> + sparc32_ipi_ops->cross_call(func, cpu_online_mask,
> arg1, arg2, arg3, arg4);
> }
>
> diff --git a/arch/sparc/kernel/kernel.h b/arch/sparc/kernel/kernel.h
> index a8fb7c0bf053..36747e8f7e36 100644
> --- a/arch/sparc/kernel/kernel.h
> +++ b/arch/sparc/kernel/kernel.h
> @@ -4,6 +4,7 @@
>
> #include <linux/interrupt.h>
> #include <linux/ftrace.h>
> +#include <linux/smp.h>
>
> #include <asm/traps.h>
> #include <asm/head.h>
> @@ -75,6 +76,16 @@ int sparc32_classify_syscall(unsigned int syscall);
> #endif
>
> #ifdef CONFIG_SPARC32
> +
> +#ifdef CONFIG_SMP
> +static inline bool cpu_for_ipi(const cpumask_t *mask, unsigned int cpu)
> +{
> + return cpumask_test_cpu(cpu, mask) &&
> + cpumask_test_cpu(cpu, cpu_online_mask) &&
> + cpu != smp_processor_id();
> +}
> +#endif /* CONFIG_SMP */
> +
> /* setup_32.c */
> struct linux_romvec;
> void sparc32_start_kernel(struct linux_romvec *rp);
> diff --git a/arch/sparc/kernel/leon_smp.c b/arch/sparc/kernel/leon_smp.c
> index 1ee393abc463..291884c8d82a 100644
> --- a/arch/sparc/kernel/leon_smp.c
> +++ b/arch/sparc/kernel/leon_smp.c
> @@ -372,7 +372,7 @@ static struct smp_funcall {
> static DEFINE_SPINLOCK(cross_call_lock);
>
> /* Cross calls must be serialized, at least currently. */
> -static void leon_cross_call(void *func, cpumask_t mask, unsigned long arg1,
> +static void leon_cross_call(void *func, const cpumask_t *mask, unsigned long arg1,
> unsigned long arg2, unsigned long arg3,
> unsigned long arg4)
> {
> @@ -403,14 +403,11 @@ static void leon_cross_call(void *func, cpumask_t mask, unsigned long arg1,
> {
> register int i;
>
> - cpumask_clear_cpu(smp_processor_id(), &mask);
> - cpumask_and(&mask, cpu_online_mask, &mask);
> for (i = 0; i <= high; i++) {
> - if (cpumask_test_cpu(i, &mask)) {
> + if (cpu_for_ipi(mask, i)) {
> ccall_info.processors_in[i] = 0;
> ccall_info.processors_out[i] = 0;
> leon_send_ipi(i, LEON3_IRQ_CROSS_CALL);
> -
> }
> }
> }
> @@ -420,7 +417,7 @@ static void leon_cross_call(void *func, cpumask_t mask, unsigned long arg1,
>
> i = 0;
> do {
> - if (!cpumask_test_cpu(i, &mask))
> + if (!cpu_for_ipi(mask, i))
> continue;
>
> while (!ccall_info.processors_in[i])
> @@ -429,7 +426,7 @@ static void leon_cross_call(void *func, cpumask_t mask, unsigned long arg1,
>
> i = 0;
> do {
> - if (!cpumask_test_cpu(i, &mask))
> + if (!cpu_for_ipi(mask, i))
> continue;
>
> while (!ccall_info.processors_out[i])
> diff --git a/arch/sparc/kernel/sun4d_smp.c b/arch/sparc/kernel/sun4d_smp.c
> index 9a62a5cf3337..7dc57ca05728 100644
> --- a/arch/sparc/kernel/sun4d_smp.c
> +++ b/arch/sparc/kernel/sun4d_smp.c
> @@ -281,7 +281,7 @@ static struct smp_funcall {
> static DEFINE_SPINLOCK(cross_call_lock);
>
> /* Cross calls must be serialized, at least currently. */
> -static void sun4d_cross_call(void *func, cpumask_t mask, unsigned long arg1,
> +static void sun4d_cross_call(void *func, const cpumask_t *mask, unsigned long arg1,
> unsigned long arg2, unsigned long arg3,
> unsigned long arg4)
> {
> @@ -315,10 +315,8 @@ static void sun4d_cross_call(void *func, cpumask_t mask, unsigned long arg1,
> {
> register int i;
>
> - cpumask_clear_cpu(smp_processor_id(), &mask);
> - cpumask_and(&mask, cpu_online_mask, &mask);
> for (i = 0; i <= high; i++) {
> - if (cpumask_test_cpu(i, &mask)) {
> + if (cpu_for_ipi(mask, i)) {
> ccall_info.processors_in[i] = 0;
> ccall_info.processors_out[i] = 0;
> sun4d_send_ipi(i, IRQ_CROSS_CALL);
> @@ -331,7 +329,7 @@ static void sun4d_cross_call(void *func, cpumask_t mask, unsigned long arg1,
>
> i = 0;
> do {
> - if (!cpumask_test_cpu(i, &mask))
> + if (!cpu_for_ipi(mask, i))
> continue;
> while (!ccall_info.processors_in[i])
> barrier();
> @@ -339,7 +337,7 @@ static void sun4d_cross_call(void *func, cpumask_t mask, unsigned long arg1,
>
> i = 0;
> do {
> - if (!cpumask_test_cpu(i, &mask))
> + if (!cpu_for_ipi(mask, i))
> continue;
> while (!ccall_info.processors_out[i])
> barrier();
> diff --git a/arch/sparc/kernel/sun4m_smp.c b/arch/sparc/kernel/sun4m_smp.c
> index 056df034e79e..3f43f64e3489 100644
> --- a/arch/sparc/kernel/sun4m_smp.c
> +++ b/arch/sparc/kernel/sun4m_smp.c
> @@ -170,7 +170,7 @@ static struct smp_funcall {
> static DEFINE_SPINLOCK(cross_call_lock);
>
> /* Cross calls must be serialized, at least currently. */
> -static void sun4m_cross_call(void *func, cpumask_t mask, unsigned long arg1,
> +static void sun4m_cross_call(void *func, const cpumask_t *mask, unsigned long arg1,
> unsigned long arg2, unsigned long arg3,
> unsigned long arg4)
> {
> @@ -191,10 +191,8 @@ static void sun4m_cross_call(void *func, cpumask_t mask, unsigned long arg1,
> {
> register int i;
>
> - cpumask_clear_cpu(smp_processor_id(), &mask);
> - cpumask_and(&mask, cpu_online_mask, &mask);
> for (i = 0; i < ncpus; i++) {
> - if (cpumask_test_cpu(i, &mask)) {
> + if (cpu_for_ipi(mask, i)) {
> ccall_info.processors_in[i] = 0;
> ccall_info.processors_out[i] = 0;
> sun4m_send_ipi(i, IRQ_CROSS_CALL);
> @@ -210,7 +208,7 @@ static void sun4m_cross_call(void *func, cpumask_t mask, unsigned long arg1,
>
> i = 0;
> do {
> - if (!cpumask_test_cpu(i, &mask))
> + if (!cpu_for_ipi(mask, i))
> continue;
> while (!ccall_info.processors_in[i])
> barrier();
> @@ -218,7 +216,7 @@ static void sun4m_cross_call(void *func, cpumask_t mask, unsigned long arg1,
>
> i = 0;
> do {
> - if (!cpumask_test_cpu(i, &mask))
> + if (!cpu_for_ipi(mask, i))
> continue;
> while (!ccall_info.processors_out[i])
> barrier();
> --
> 2.27.0
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