Re: [Xen-devel] [PATCH] xen/xenoprof: avoid division by 0

[Tim Deegan <tim@xxxxxxx>]

At 16:34 +0000 on 14 Feb (1360859678), Jan Beulich wrote:
> >>> On 14.02.13 at 17:16, Tim Deegan <tim@xxxxxxx> wrote:
> > --- a/xen/common/xenoprof.c Thu Feb 14 15:46:56 2013 +0000
> > +++ b/xen/common/xenoprof.c Thu Feb 14 16:16:17 2013 +0000
> > @@ -225,7 +225,7 @@ static int alloc_xenoprof_struct(
> >  #endif
> >  
> >      /* reduce max_samples if necessary to limit pages allocated */
> > -    max_bufsize = (MAX_OPROF_SHARED_PAGES * PAGE_SIZE) / nvcpu;
> > +    max_bufsize = (MAX_OPROF_SHARED_PAGES * PAGE_SIZE) / (nvcpu ?: 1);
> >      max_max_samples = ( (max_bufsize - bufsize) / i ) + 1;
> >      if ( (unsigned)max_samples > max_max_samples )
> >          max_samples = max_max_samples;
> 
> I think the function would better return an error in that case. After
> all there's little point in setting up anything when we for sure don't
> know how many vCPU-s a domain is going to have.

Grand so:

# HG changeset patch
# Parent 5a84cc531072378e6e5ff89b4c0e9a35000dc56f
xen/xenoprof: avoid division by 0.

Signed-off-by: Tim Deegan <tim@xxxxxxx>

diff -r 5a84cc531072 xen/common/xenoprof.c
--- a/xen/common/xenoprof.c     Thu Feb 14 15:46:56 2013 +0000
+++ b/xen/common/xenoprof.c     Thu Feb 14 16:48:49 2013 +0000
@@ -213,6 +213,9 @@ static int alloc_xenoprof_struct(
     for_each_vcpu ( d, v )
         nvcpu++;
 
+    if ( !nvcpu )
+        return -EINVAL;
+
     bufsize = sizeof(struct xenoprof_buf);
     i = sizeof(struct event_log);
 #ifdef CONFIG_COMPAT

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