From: Yury Norov <yury.norov@gmail.com>
To: Dawei Li <dawei.li@shingroup.cn>
Cc: Sam Ravnborg <sam@ravnborg.org>,
davem@davemloft.net, andreas@gaisler.com,
sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/5] Remove onstack cpumask var usage
Date: Fri, 19 Apr 2024 15:13:49 -0700 [thread overview]
Message-ID: <ZiLsnWCwKeg4B65a@yury-ThinkPad> (raw)
In-Reply-To: <A60F94A9589C8589+ZiI4yj073cgmt5Qq@centos8>
On Fri, Apr 19, 2024 at 05:26:34PM +0800, Dawei Li wrote:
> Hi Sam,
>
> Thanks for the review.
>
> On Fri, Apr 19, 2024 at 07:13:50AM +0200, Sam Ravnborg wrote:
> > Hi Dawei,
> >
> > On Thu, Apr 18, 2024 at 06:49:44PM +0800, Dawei Li wrote:
> > > Hi,
> > >
> > > This series aims at removing on-stack cpumask var usage for sparc arch.
> > >
> > > Generally 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.
> >
> > Took a quick look at the patches, looks good except the one the bot
> > already complained about.
>
> I will fix this building warning in respinning.
>
> > A quick grep shows a few more cases where we have an on-stack cpumask
> > in sparc code.
> >
> > kernel/ds.c: cpumask_t mask;
>
> About this case, it's kinda tricky for:
> - dr_cpu_data() returns void, so alloc_cpumask_var() is no go.
>
> - No idea of the calling context of dr_cpu_data(). IIUC,
> dr_cpu_data()
> ->dr_cpu_configure()
> ->kzalloc(resp_len, GFP_KERNEL)
> So I guess it's in process context?
> If consumption above is OK, a simple but _ugly_ solution could be:
>
> diff --git a/arch/sparc/kernel/ds.c b/arch/sparc/kernel/ds.c
> index ffdc15588ac2..c9e4ebdccf49 100644
> --- a/arch/sparc/kernel/ds.c
> +++ b/arch/sparc/kernel/ds.c
> @@ -634,7 +634,8 @@ static void dr_cpu_data(struct ds_info *dp, struct ds_cap_state *cp, void *buf,
> struct dr_cpu_tag *tag = (struct dr_cpu_tag *) (data + 1);
> u32 *cpu_list = (u32 *) (tag + 1);
> u64 req_num = tag->req_num;
> - cpumask_t mask;
> + static DEFINE_MUTEX(mask_lock);
> + static cpumask_t mask;
> unsigned int i;
> int err;
>
> @@ -651,6 +652,8 @@ static void dr_cpu_data(struct ds_info *dp, struct ds_cap_state *cp, void *buf,
>
> purge_dups(cpu_list, tag->num_records);
>
> + mutex_lock(&mask_lock);
> +
> cpumask_clear(&mask);
> for (i = 0; i < tag->num_records; i++) {
> if (cpu_list[i] == CPU_SENTINEL)
> @@ -665,6 +668,8 @@ static void dr_cpu_data(struct ds_info *dp, struct ds_cap_state *cp, void *buf,
> else
> err = dr_cpu_unconfigure(dp, cp, req_num, &mask);
>
> + mutex_unlock(&mask_lock);
> +
> if (err)
> dr_cpu_send_error(dp, cp, data);
> }
>
> How does it sound to you?
>
> > kernel/leon_kernel.c: cpumask_t mask;
>
> It's in irqchip::irq_set_affinity(), which is in atomic context(raw spinlock(s) held),
> so dynamic allocation is not a good idea.
>
> My proposal(*untested*) is somewhat complicated for it introduces a new helper.
>
> diff --git a/arch/sparc/kernel/leon_kernel.c b/arch/sparc/kernel/leon_kernel.c
> index 4c61da491fee..6eced7acb8bc 100644
> --- a/arch/sparc/kernel/leon_kernel.c
> +++ b/arch/sparc/kernel/leon_kernel.c
> @@ -104,15 +104,25 @@ unsigned long leon_get_irqmask(unsigned int irq)
> }
>
> #ifdef CONFIG_SMP
> +
> +static bool cpumask_include(const struct cpumask *srcp1, const struct cpumask *srcp2)
Don't steal the other's subsystems prefixes.
> +{
> + unsigned int cpu;
> +
> + for_each_cpu(cpu, srcp2) {
> + if (!cpumask_test_cpu(cpu, srcp1))
> + return false;
> + }
> +
> + return true;
> +}
We've got cpumask_subset() for this.
> static int irq_choose_cpu(const struct cpumask *affinity)
> {
> - cpumask_t mask;
> + unsigned int cpu = cpumask_first_and(affinity, cpu_online_mask);
>
> - cpumask_and(&mask, cpu_online_mask, affinity);
> - if (cpumask_equal(&mask, cpu_online_mask) || cpumask_empty(&mask))
> - return boot_cpu_id;
> - else
> - return cpumask_first(&mask);
> + return cpumask_include(affinity, cpu_online_mask) || cpu >= nr_cpu_ids ?
> + boot_cpu_id : cpu;
> }
> #else
> #define irq_choose_cpu(affinity) boot_cpu_id
>
> Is it OK?
>
> [cc Yury for bitmap API]
>
> > kernel/leon_smp.c:static void leon_cross_call(void *func, cpumask_t mask, unsigned long arg1,
> > kernel/sun4d_smp.c:static void sun4d_cross_call(void *func, cpumask_t mask, unsigned long arg1,
>
> Actually I am awared of existence of (at least some of) them, but so far I
> have not found a _proper_ way of dealing with them(especially for case of
> ds.c).
>
> Please lemme dig into it.
>
> Thanks,
>
> Dawei
>
> >
> > Do you plan to look at the other on-stack users too?
> > It would be nice to see them all gone in one patch-set.
> >
> > Sam
> >
prev parent reply other threads:[~2024-04-19 22:13 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-18 10:49 [PATCH 0/5] Remove onstack cpumask var usage Dawei Li
2024-04-18 10:49 ` [PATCH 1/5] sparc/srmmu: Remove on-stack cpumask var Dawei Li
2024-04-18 10:49 ` [PATCH 2/5] sparc/irq: " Dawei Li
2024-04-19 0:19 ` kernel test robot
2024-04-18 10:49 ` [PATCH 3/5] sparc/of: " Dawei Li
2024-04-18 10:49 ` [PATCH 4/5] sparc/pci_msi: " Dawei Li
2024-04-18 10:49 ` [PATCH 5/5] sparc: " Dawei Li
2024-04-19 5:13 ` [PATCH 0/5] Remove onstack cpumask var usage Sam Ravnborg
2024-04-19 9:26 ` Dawei Li
2024-04-19 20:33 ` Sam Ravnborg
2024-04-19 22:13 ` Yury Norov [this message]
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