linux-kernel - Re: [PATCH] s390/hypfs: Use kmalloc_array() in diag0c

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Date:   Thu, 1 Sep 2016 18:53:25 +0200
From:   Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        SF Markus Elfring <elfring@...rs.sourceforge.net>,
        linux-s390@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH] s390/hypfs: Use kmalloc_array() in diag0c_store()

Am Thu, 1 Sep 2016 17:39:02 +0200
schrieb Paolo Bonzini <pbonzini@...hat.com>:

> 
> 
> On 01/09/2016 12:32, Heiko Carstens wrote:
> > On Thu, Sep 01, 2016 at 11:38:15AM +0200, SF Markus Elfring wrote:
> >> From: Markus Elfring <elfring@...rs.sourceforge.net>
> >> Date: Thu, 1 Sep 2016 11:30:58 +0200
> >>
> >> A multiplication for the size determination of a memory allocation
> >> indicated that an array data structure should be processed.
> >> Thus use the corresponding function "kmalloc_array".
> >>
> >> This issue was detected by using the Coccinelle software.
> >>
> >> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> >> ---
> >>  arch/s390/hypfs/hypfs_diag0c.c | 4 +++-
> >>  1 file changed, 3 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/arch/s390/hypfs/hypfs_diag0c.c
> >> b/arch/s390/hypfs/hypfs_diag0c.c index 0f1927c..61418a8 100644
> >> --- a/arch/s390/hypfs/hypfs_diag0c.c
> >> +++ b/arch/s390/hypfs/hypfs_diag0c.c
> >> @@ -48,7 +48,9 @@ static void *diag0c_store(unsigned int *count)
> >>  
> >>  	get_online_cpus();
> >>  	cpu_count = num_online_cpus();
> >> -	cpu_vec = kmalloc(sizeof(*cpu_vec) * num_possible_cpus(),
> >> GFP_KERNEL);
> >> +	cpu_vec = kmalloc_array(num_possible_cpus(),
> >> +				sizeof(*cpu_vec),
> >> +				GFP_KERNEL);
> > 
> > How does this improve the situation? For any real life scenario
> > this can't overflow, but it does add an extra (pointless) runtime
> > check, since num_possible_cpus() is not a compile time constant.
> > 
> > So, why is this an "issue"?
> 
> It's not an issue but I for one still prefer consistent use of
> kmalloc_array and kcalloc.

Hello Paolo,

I will keep this in mind for future code, but would prefer not changing
this now.

Michael