Messages in this thread | | | Date | Fri, 27 Jun 2008 19:24:59 +0200 | From | "Vegard Nossum" <> | Subject | Re: [PATCH 1/1] x86: Add check for node passed to node_to_cpumask V3 |
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On Fri, Jun 27, 2008 at 7:10 PM, Mike Travis <travis@sgi.com> wrote: > Subject: [PATCH 1/1] x86: Add check for node passed to node_to_cpumask V3 > > * When CONFIG_DEBUG_PER_CPU_MAPS is set, the node passed to > node_to_cpumask and node_to_cpumask_ptr should be validated. > If invalid, then a dump_stack is performed and a zero cpumask > is returned. > > Based on "Fri Jun 27 10:06:06 PDT 2008" tip/master... ;-) > > Signed-off-by: Mike Travis <travis@sgi.com> > --- > V2: Slightly different version to remove a compiler warning. > V3: Redone to reflect moving setup.c -> setup_percpu.c > --- > arch/x86/kernel/setup_percpu.c | 26 +++++++++++++++++++++++--- > include/asm-x86/topology.h | 7 ++++++- > 2 files changed, 29 insertions(+), 4 deletions(-) > > --- linux-2.6.tip.orig/arch/x86/kernel/setup_percpu.c > +++ linux-2.6.tip/arch/x86/kernel/setup_percpu.c > @@ -346,6 +346,10 @@ int early_cpu_to_node(int cpu) > return per_cpu(x86_cpu_to_node_map, cpu); > } > > + > +/* empty cpumask */ > +static const cpumask_t cpu_mask_none; > + > /* > * Returns a pointer to the bitmask of CPUs on Node 'node'. > */ > @@ -358,13 +362,23 @@ cpumask_t *_node_to_cpumask_ptr(int node > dump_stack(); > return &cpu_online_map; > } > - BUG_ON(node >= nr_node_ids); > - return &node_to_cpumask_map[node]; > + if (node >= nr_node_ids) { > + printk(KERN_WARNING > + "_node_to_cpumask_ptr(%d): node > nr_node_ids(%d)\n", > + node, nr_node_ids); > + dump_stack(); > + return (cpumask_t *)&cpu_mask_none;
Hm, I am wondering about this.
There exists an option DEBUG_RODATA ("Write protect kernel read-only data structures"). I'm guessing this RO protections means that we'll get page faults (and thus BUG/panic) if this "none" mask is ever attempted to be changed.
So if CONFIG_DEBUG_RODATA=y, I believe we'll see first this warning, then a panic (after all). Would it be better to make cpu_mask_none non-const, in spirit of trying to continue as far as possible? I don't really know if it matters, though. It seems that fedora kernels at least ship with a default of DEBUG_RODATA=y.
What you could also do is to make it non-const and then zero it each time it is requested. Again, this is an error situation in either case, so maybe it's not worth fussing about.
Vegard
-- "The animistic metaphor of the bug that maliciously sneaked in while the programmer was not looking is intellectually dishonest as it disguises that the error is the programmer's own creation." -- E. W. Dijkstra, EWD1036
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