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

[Tim Deegan <tim@xen.org>]

At 17:05 +0000 on 14 Feb (1360861530), Jan Beulich wrote:
> >>> On 14.02.13 at 17:50, Tim Deegan <tim@xen.org> wrote:
> > At 16:34 +0000 on 14 Feb (1360859678), Jan Beulich wrote:
> >> >>> On 14.02.13 at 17:16, Tim Deegan <tim@xen.org> 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@xen.org>
> > 
> > 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;
> 
> Missing some cleanup here? Or move the preceding loop and this
> addition to the top of the function?

D'oh, yes.  Trying again:

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

Signed-off-by: Tim Deegan <tim@xen.org>

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 17:07:41 2013 +0000
@@ -193,6 +193,13 @@ static int alloc_xenoprof_struct(
     unsigned max_max_samples;
     int i;
 
+    nvcpu = 0;
+    for_each_vcpu ( d, v )
+        nvcpu++;
+
+    if ( !nvcpu )
+        return -EINVAL;
+
     d->xenoprof = xzalloc(struct xenoprof);
     if ( d->xenoprof == NULL )
     {
@@ -209,10 +216,6 @@ static int alloc_xenoprof_struct(
         return -ENOMEM;
     }
 
-    nvcpu = 0;
-    for_each_vcpu ( d, v )
-        nvcpu++;
-
     bufsize = sizeof(struct xenoprof_buf);
     i = sizeof(struct event_log);
 #ifdef CONFIG_COMPAT