Message-ID: <YqHIEthhhi5e+Mtb@alley>
Date:   Thu, 9 Jun 2022 12:14:42 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     ink@...assic.park.msu.ru, mattst88@...il.com, vgupta@...nel.org,
        linux@...linux.org.uk, ulli.kroll@...glemail.com,
        linus.walleij@...aro.org, shawnguo@...nel.org,
        Sascha Hauer <s.hauer@...gutronix.de>, kernel@...gutronix.de,
        festevam@...il.com, linux-imx@....com, tony@...mide.com,
        khilman@...nel.org, catalin.marinas@....com, will@...nel.org,
        guoren@...nel.org, bcain@...cinc.com, chenhuacai@...nel.org,
        kernel@...0n.name, geert@...ux-m68k.org, sammy@...my.net,
        monstr@...str.eu, tsbogend@...ha.franken.de, dinguyen@...nel.org,
        jonas@...thpole.se, stefan.kristiansson@...nalahti.fi,
        shorne@...il.com, James.Bottomley@...senpartnership.com,
        deller@....de, mpe@...erman.id.au, benh@...nel.crashing.org,
        paulus@...ba.org, paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, hca@...ux.ibm.com, gor@...ux.ibm.com,
        agordeev@...ux.ibm.com, borntraeger@...ux.ibm.com,
        svens@...ux.ibm.com, ysato@...rs.sourceforge.jp, dalias@...c.org,
        davem@...emloft.net, richard@....at,
        anton.ivanov@...bridgegreys.com, johannes@...solutions.net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, jgross@...e.com, srivatsa@...il.mit.edu,
        amakhalov@...are.com, pv-drivers@...are.com,
        boris.ostrovsky@...cle.com, chris@...kel.net, jcmvbkbc@...il.com,
        rafael@...nel.org, lenb@...nel.org, pavel@....cz,
        gregkh@...uxfoundation.org, mturquette@...libre.com,
        sboyd@...nel.org, daniel.lezcano@...aro.org, lpieralisi@...nel.org,
        sudeep.holla@....com, agross@...nel.org,
        bjorn.andersson@...aro.org, anup@...infault.org,
        thierry.reding@...il.com, jonathanh@...dia.com,
        jacob.jun.pan@...ux.intel.com, Arnd Bergmann <arnd@...db.de>,
        yury.norov@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk, rostedt@...dmis.org,
        senozhatsky@...omium.org, john.ogness@...utronix.de,
        paulmck@...nel.org, frederic@...nel.org, quic_neeraju@...cinc.com,
        josh@...htriplett.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, joel@...lfernandes.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, jpoimboe@...nel.org,
        linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-perf-users@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        xen-devel@...ts.xenproject.org, linux-xtensa@...ux-xtensa.org,
        linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-arch@...r.kernel.org,
        rcu@...r.kernel.org
Subject: Re: [PATCH 24/36] printk: Remove trace_.*_rcuidle() usage

Sending again. The previous attempt was rejected by several
recipients. It was caused by a mail server changes on my side.

I am sorry for spamming those who got the 1st mail already.

On Wed 2022-06-08 16:27:47, Peter Zijlstra wrote:
> The problem, per commit fc98c3c8c9dc ("printk: use rcuidle console
> tracepoint"), was printk usage from the cpuidle path where RCU was
> already disabled.
> 
> Per the patches earlier in this series, this is no longer the case.

My understanding is that this series reduces a lot the amount
of code called with RCU disabled. As a result the particular printk()
call mentioned by commit fc98c3c8c9dc ("printk: use rcuidle console
tracepoint") is called with RCU enabled now. Hence this particular
problem is fixed better way now.

But is this true in general?
Does this "prevent" calling printk() a safe way in code with
RCU disabled?

I am not sure if anyone cares. printk() is the best effort
functionality because of the consoles code anyway. Also I wonder
if anyone uses this trace_console().

Therefore if this patch allows to remove some tricky tracing
code then it might be worth it. But if trace_console_rcuidle()
variant is still going to be available then I would keep using it.

Best Regards,
Petr

> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/printk/printk.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2238,7 +2238,7 @@ static u16 printk_sprint(char *text, u16
>  		}
>  	}
>  
> -	trace_console_rcuidle(text, text_len);
> +	trace_console(text, text_len);
>  
>  	return text_len;
>  }
> 

Powered by blists - more mailing lists