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<p>Hi Guilherme,</p>
Nice catch.<br>
<br>
<div class="moz-cite-prefix">On Friday 20 October 2017 01:11 AM,
Guilherme G. Piccoli wrote:<br>
</div>
<blockquote type="cite"
cite="mid:20171019194133.27485-1-gpiccoli@linux.vnet.ibm.com">
<pre wrap="">When setting nr_cpus=1, we observed a crash in IMC code during boot
due to a missing allocation: basically, IMC code is taking the number
of threads into account in imc_mem_init() and if we manually set
nr_cpus for a value that is not multiple of the number of threads per
core, an integer division in that function will discard the decimal
portion, leading IMC to not allocate one mem_info struct. This causes
a NULL pointer dereference later, on is_core_imc_mem_inited().
This patch just rounds that division up, fixing the bug.
Signed-off-by: Guilherme G. Piccoli <a class="moz-txt-link-rfc2396E" href="mailto:gpiccoli@linux.vnet.ibm.com"><gpiccoli@linux.vnet.ibm.com></a></pre>
</blockquote>
Acked-by: Anju T Sudhakar <a class="moz-txt-link-rfc2396E"
href="mailto:anju@linux.vnet.ibm.com"><anju@linux.vnet.ibm.com></a>
<blockquote type="cite"
cite="mid:20171019194133.27485-1-gpiccoli@linux.vnet.ibm.com">
<pre wrap="">
---
Anju, looks good to you? Tested in P9 with latest FW available.
arch/powerpc/perf/imc-pmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index 88126245881b..92ae5de0bbac 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -1104,7 +1104,7 @@ static int init_nest_pmu_ref(void)
static void cleanup_all_core_imc_memory(void)
{
- int i, nr_cores = num_present_cpus() / threads_per_core;
+ int i, nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
struct imc_mem_info *ptr = core_imc_pmu->mem_info;
int size = core_imc_pmu->counter_mem_size;
@@ -1212,7 +1212,7 @@ static int imc_mem_init(struct imc_pmu *pmu_ptr, struct device_node *parent,
if (!pmu_ptr->pmu.name)
return -ENOMEM;
- nr_cores = num_present_cpus() / threads_per_core;
+ nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
pmu_ptr->mem_info = kcalloc(nr_cores, sizeof(struct imc_mem_info),
GFP_KERNEL);
</pre>
</blockquote>
<br>
Thanks,<br>
Anju<br>
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