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-rw-r--r--lib/group_cpus.c22
1 files changed, 16 insertions, 6 deletions
diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index aa3f6815bb12..ee272c4cefcc 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -366,13 +366,25 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps)
if (!masks)
goto fail_node_to_cpumask;
- /* Stabilize the cpumasks */
- cpus_read_lock();
build_node_to_cpumask(node_to_cpumask);
+ /*
+ * Make a local cache of 'cpu_present_mask', so the two stages
+ * spread can observe consistent 'cpu_present_mask' without holding
+ * cpu hotplug lock, then we can reduce deadlock risk with cpu
+ * hotplug code.
+ *
+ * Here CPU hotplug may happen when reading `cpu_present_mask`, and
+ * we can live with the case because it only affects that hotplug
+ * CPU is handled in the 1st or 2nd stage, and either way is correct
+ * from API user viewpoint since 2-stage spread is sort of
+ * optimization.
+ */
+ cpumask_copy(npresmsk, data_race(cpu_present_mask));
+
/* grouping present CPUs first */
ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
- cpu_present_mask, nmsk, masks);
+ npresmsk, nmsk, masks);
if (ret < 0)
goto fail_build_affinity;
nr_present = ret;
@@ -387,15 +399,13 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps)
curgrp = 0;
else
curgrp = nr_present;
- cpumask_andnot(npresmsk, cpu_possible_mask, cpu_present_mask);
+ cpumask_andnot(npresmsk, cpu_possible_mask, npresmsk);
ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
npresmsk, nmsk, masks);
if (ret >= 0)
nr_others = ret;
fail_build_affinity:
- cpus_read_unlock();
-
if (ret >= 0)
WARN_ON(nr_present + nr_others < numgrps);