[PATCH 1/1] block: Range check cpu in blk_cpu_to_group

From: Brian King
Date: Thu Sep 09 2010 - 13:41:45 EST



While testing CPU DLPAR, the following problem was discovered.
We were DLPAR removing the first CPU, which in this case was
logical CPUs 0-3. CPUs 0-2 were already marked offline and
we were in the process of offlining CPU 3. After marking
the CPU inactive and offline in cpu_disable, but before the
cpu was completely idle (cpu_die), we ended up in __make_request
on CPU 3. There we looked at the topology map to see which CPU
to complete the I/O on and found no CPUs in the cpu_sibling_map.
This resulted in the block layer setting the completion cpu
to be NR_CPUS, which then caused an oops when we tried to
complete the I/O.

Fix this by sanity checking the value we return from blk_cpu_to_group
to be a valid cpu value.

Signed-off-by: Brian King <brking@xxxxxxxxxxxxxxxxxx>
---

block/blk.h | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff -puN block/blk.h~blk_cpu_to_group_range_fix block/blk.h
--- linux-2.6/block/blk.h~blk_cpu_to_group_range_fix 2010-08-31 09:12:18.000000000 -0500
+++ linux-2.6-bjking1/block/blk.h 2010-08-31 16:48:17.000000000 -0500
@@ -142,14 +142,19 @@ static inline int queue_congestion_off_t

static inline int blk_cpu_to_group(int cpu)
{
+ int group = NR_CPUS;
#ifdef CONFIG_SCHED_MC
const struct cpumask *mask = cpu_coregroup_mask(cpu);
- return cpumask_first(mask);
+ group = cpumask_first(mask);
#elif defined(CONFIG_SCHED_SMT)
- return cpumask_first(topology_thread_cpumask(cpu));
+ group = cpumask_first(topology_thread_cpumask(cpu));
#else
return cpu;
#endif
+
+ if (likely(group < NR_CPUS))
+ return group;
+ return cpu;
}

/*
_
--
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