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Subject: Re: [PATCH] x86/xen: Improve failed hypercall debugging
To: Andy Lutomirski <luto@kernel.org>, xen-devel@lists.xenproject.org
References: <1eda2acc5ed68b41f24ba7ab2672976fd92a7f9e.1493747901.git.luto@kernel.org>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
        Juergen Gross <jgross@suse.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <bd5e18dd-415c-26cf-f88f-eb437a3731fc@oracle.com>
Date: Tue, 2 May 2017 14:28:54 -0400
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On 05/02/2017 01:59 PM, Andy Lutomirski wrote:
> When fiddling with xen_exit_mmap(), I noticed that failed multicall
> debugging doesn't work if the multicall is just one call.  Fix it.

That wouldn't be a multicall though, we'll end up making the desired
hypercall directly.

Besides,  b->debug[] is not initialized in this case.

-boris

>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>  arch/x86/xen/multicalls.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
> index ea54a08d8301..b6b3f024d342 100644
> --- a/arch/x86/xen/multicalls.c
> +++ b/arch/x86/xen/multicalls.c
> @@ -96,23 +96,23 @@ void xen_mc_flush(void)
>  		for (i = 0; i < b->mcidx; i++)
>  			if (b->entries[i].result < 0)
>  				ret++;
> +	}
>  
>  #if MC_DEBUG
> -		if (ret) {
> -			printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
> -			       ret, smp_processor_id());
> -			dump_stack();
> -			for (i = 0; i < b->mcidx; i++) {
> -				printk(KERN_DEBUG "  call %2d/%d: op=%lu arg=[%lx] result=%ld\t%pF\n",
> -				       i+1, b->mcidx,
> -				       b->debug[i].op,
> -				       b->debug[i].args[0],
> -				       b->entries[i].result,
> -				       b->caller[i]);
> -			}
> +	if (ret) {
> +		printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
> +		       ret, smp_processor_id());
> +		dump_stack();
> +		for (i = 0; i < b->mcidx; i++) {
> +			printk(KERN_DEBUG "  call %2d/%d: op=%lu arg=[%lx] result=%ld\t%pF\n",
> +			       i+1, b->mcidx,
> +			       b->debug[i].op,
> +			       b->debug[i].args[0],
> +			       b->entries[i].result,
> +			       b->caller[i]);
>  		}
> -#endif
>  	}
> +#endif
>  
>  	b->mcidx = 0;
>  	b->argidx = 0;