Re: [PATCH v7 3/6] powerpc/perf: consolidate read_user_stack_32

From: Michael Ellerman <mpe@ellerman.id.au>
To: Michal Suchanek <msuchanek@suse.de>, linuxppc-dev@lists.ozlabs.org
Cc: Michal Suchanek <msuchanek@suse.de>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Nicholas Piggin <npiggin@gmail.com>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
	Breno Leitao <leitao@debian.org>, Arnd Bergmann <arnd@arndb.de>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Firoz Khan <firoz.khan@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Joel Stanley <joel@jms.id.au>,
	Hari Bathini <hbathini@linux.ibm.com>,
	Michael Neuling <mikey@neuling.org>,
	Andrew Donnellan <andrew.donnellan@au1.ibm.com>,
	Russell Currey <ruscur@russell.cc>,
	Diana Craciun <diana.craciun@nxp.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	David Hildenbrand <david@redhat.com>,
	Allison Randal <allison@lohutok.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v7 3/6] powerpc/perf: consolidate read_user_stack_32
Date: Mon, 02 Sep 2019 13:53:21 +1000	[thread overview]
Message-ID: <87a7bntkum.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <ea3783a1640b707ef9ce4740562850ef1152829b.1567198491.git.msuchanek@suse.de>

Michal Suchanek <msuchanek@suse.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@suse.de>
> Reviewed-by: Christophe Leroy <christophe.leroy@c-s.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