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Subject[GIT pull] cpu hotplug updates for 4.14
Linus,

please pull the latest smp-hotplug-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git smp-hotplug-for-linus

A single fix to handle the removal of the first dynamic CPU hotplug state
correctly.

Thanks,

tglx

------------------>
Ethan Barnes (1):
smp/hotplug: Handle removal correctly in cpuhp_store_callbacks()


kernel/cpu.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index eee033134262..a88c29ab09be 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1252,7 +1252,17 @@ static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
struct cpuhp_step *sp;
int ret = 0;

- if (state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN) {
+ /*
+ * If name is NULL, then the state gets removed.
+ *
+ * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
+ * the first allocation from these dynamic ranges, so the removal
+ * would trigger a new allocation and clear the wrong (already
+ * empty) state, leaving the callbacks of the to be cleared state
+ * dangling, which causes wreckage on the next hotplug operation.
+ */
+ if (name && (state == CPUHP_AP_ONLINE_DYN ||
+ state == CPUHP_BP_PREPARE_DYN)) {
ret = cpuhp_reserve_state(state);
if (ret < 0)
return ret;
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