On 9/5/2018 5:03 PM, Thomas Gleixner wrote:
On Tue, 4 Sep 2018, Neeraj Upadhyay wrote:
If takedown_cpu() fails during _cpu_down(), st->state is reset,
by calling cpuhp_reset_state(). This results in an additional
increment of st->state, which results in CPUHP_AP_SMPBOOT_THREADS
state being skipped during rollback. Fix this by not calling
cpuhp_reset_state() and doing the state reset directly in
_cpu_down().
Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core")
Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
---
kernel/cpu.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85..9f49edb 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -970,7 +970,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
*/
ret = cpuhp_down_callbacks(cpu, st, target);
if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) {
- cpuhp_reset_state(st, prev_state);
+ /*
+ * As st->last is not set, cpuhp_reset_state() increments
+ * st->state, which results in CPUHP_AP_SMPBOOT_THREADS being
+ * skipped during rollback. So, don't use it here.
+ */
+ st->rollback = true;
+ st->target = prev_state;
+ st->bringup = !st->bringup;
No, this is just papering over the actual problem.
The state inconsistency happens in take_cpu_down() when it returns with a
failure from __cpu_disable() because that returns with state = TEARDOWN_CPU
and st->state is then incremented in undo_cpu_down().
That's the real issue and we need to analyze the whole cpu_down rollback
logic first.
Could this be done like below ?
diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85..47bce90 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -802,17 +802,18 @@ static int take_cpu_down(void *_param)
int err, cpu = smp_processor_id();
int ret;
- /* Ensure this CPU doesn't handle any more interrupts. */
- err = __cpu_disable();
- if (err < 0)
- return err;
-
/*
* We get here while we are in CPUHP_TEARDOWN_CPU state and we
must not
* do this step again.
*/
WARN_ON(st->state != CPUHP_TEARDOWN_CPU);
st->state--;
+
+ /* Ensure this CPU doesn't handle any more interrupts. */
+ err = __cpu_disable();
+ if (err < 0)
+ return err;
+
/* Invoke the former CPU_DYING callbacks */
Thanks,
Mukesh
