linux-kernel - Re: [PATCH v7 3/6] powerpc/perf: consolidate read_user_stack

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Message-ID: <87a7bntkum.fsf@mpe.ellerman.id.au>
Date:   Mon, 02 Sep 2019 13:53:21 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Michal Suchanek <msuchanek@...e.de>, linuxppc-dev@...ts.ozlabs.org
Cc:     Michal Suchanek <msuchanek@...e.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        Breno Leitao <leitao@...ian.org>,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Firoz Khan <firoz.khan@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joel Stanley <joel@....id.au>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Michael Neuling <mikey@...ling.org>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        Russell Currey <ruscur@...sell.cc>,
        Diana Craciun <diana.craciun@....com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        David Hildenbrand <david@...hat.com>,
        Allison Randal <allison@...utok.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v7 3/6] powerpc/perf: consolidate read_user_stack_32

Michal Suchanek <msuchanek@...e.de> writes:

> There are two almost identical copies for 32bit and 64bit.
>
> The function is used only in 32bit code which will be split out in next
> patch so consolidate to one function.
>
> Signed-off-by: Michal Suchanek <msuchanek@...e.de>
> Reviewed-by: Christophe Leroy <christophe.leroy@....fr>
> ---
> new patch in v6
> ---
>  arch/powerpc/perf/callchain.c | 25 +++++++++----------------
>  1 file changed, 9 insertions(+), 16 deletions(-)
>
> diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
> index c84bbd4298a0..b7cdcce20280 100644
> --- a/arch/powerpc/perf/callchain.c
> +++ b/arch/powerpc/perf/callchain.c
> @@ -165,22 +165,6 @@ static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
>  	return read_user_stack_slow(ptr, ret, 8);
>  }
>  
> -static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
> -{
> -	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> -	    ((unsigned long)ptr & 3))
> -		return -EFAULT;
> -
> -	pagefault_disable();
> -	if (!__get_user_inatomic(*ret, ptr)) {
> -		pagefault_enable();
> -		return 0;
> -	}
> -	pagefault_enable();
> -
> -	return read_user_stack_slow(ptr, ret, 4);
> -}
> -
>  static inline int valid_user_sp(unsigned long sp, int is_64)
>  {
>  	if (!sp || (sp & 7) || sp > (is_64 ? TASK_SIZE : 0x100000000UL) - 32)
> @@ -295,6 +279,12 @@ static inline int current_is_64bit(void)
>  }
>  
>  #else  /* CONFIG_PPC64 */
> +static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_PPC64 */

Ending the PPC64 else case here, and then restarting it below with an
ifndef means we end up with two parts of the file that define 32-bit
code, with a common chunk in the middle, which I dislike.

I'd rather you add the empty read_user_stack_slow() in the existing
#else section and then move read_user_stack_32() below the whole ifdef
PPC64/else/endif section.

Is there some reason that doesn't work?

cheers

> @@ -313,9 +303,12 @@ static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
>  	rc = __get_user_inatomic(*ret, ptr);
>  	pagefault_enable();
>  
> +	if (IS_ENABLED(CONFIG_PPC64) && rc)
> +		return read_user_stack_slow(ptr, ret, 4);
>  	return rc;
>  }
>  
> +#ifndef CONFIG_PPC64
>  static inline void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry,
>  					  struct pt_regs *regs)
>  {
> -- 
> 2.22.0