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Subject[PATCH 2/7] smp/hotplug: Allow external multi-instance rollback
Currently the rollback of multi-instance states is handled inside
cpuhp_invoke_callback(). The problem is that when we want to allow an
explicit state change for rollback, we need to return from the
function without doing the rollback.

Change cpuhp_invoke_callback() to optionally return the multi-instance
state, such that rollback can be done from a subsequent call.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/cpu.c | 47 ++++++++++++++++++++++++++++++++---------------
1 file changed, 32 insertions(+), 15 deletions(-)

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -123,13 +123,16 @@ static struct cpuhp_step *cpuhp_get_step
/**
* cpuhp_invoke_callback _ Invoke the callbacks for a given state
* @cpu: The cpu for which the callback should be invoked
- * @step: The step in the state machine
+ * @state: The state to do callbacks for
* @bringup: True if the bringup callback should be invoked
+ * @node: For multi-instance, do a single entry callback for install/remove
+ * @lastp: For multi-instance rollback, remember how far we got
*
* Called from cpu hotplug and from the state register machinery.
*/
static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
- bool bringup, struct hlist_node *node)
+ bool bringup, struct hlist_node *node,
+ struct hlist_node **lastp)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
struct cpuhp_step *step = cpuhp_get_step(state);
@@ -138,6 +141,7 @@ static int cpuhp_invoke_callback(unsigne
int ret, cnt;

if (!step->multi_instance) {
+ WARN_ON_ONCE(lastp && *lastp);
cb = bringup ? step->startup.single : step->teardown.single;
if (!cb)
return 0;
@@ -152,6 +156,7 @@ static int cpuhp_invoke_callback(unsigne

/* Single invocation for instance add/remove */
if (node) {
+ WARN_ON_ONCE(lastp && *lastp);
trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
ret = cbm(cpu, node);
trace_cpuhp_exit(cpu, st->state, state, ret);
@@ -161,13 +166,23 @@ static int cpuhp_invoke_callback(unsigne
/* State transition. Invoke on all instances */
cnt = 0;
hlist_for_each(node, &step->list) {
+ if (lastp && node == *lastp)
+ break;
+
trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
ret = cbm(cpu, node);
trace_cpuhp_exit(cpu, st->state, state, ret);
- if (ret)
- goto err;
+ if (ret) {
+ if (!lastp)
+ goto err;
+
+ *lastp = node;
+ return ret;
+ }
cnt++;
}
+ if (lastp)
+ *lastp = NULL;
return 0;
err:
/* Rollback the instances if one failed */
@@ -323,7 +338,7 @@ static void undo_cpu_down(unsigned int c
struct cpuhp_step *step = cpuhp_get_step(st->state);

if (!step->skip_onerr)
- cpuhp_invoke_callback(cpu, st->state, true, NULL);
+ cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
}
}

@@ -334,7 +349,7 @@ static int cpuhp_down_callbacks(unsigned
int ret = 0;

for (; st->state > target; st->state--) {
- ret = cpuhp_invoke_callback(cpu, st->state, false, NULL);
+ ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
if (ret) {
st->target = prev_state;
undo_cpu_down(cpu, st);
@@ -350,7 +365,7 @@ static void undo_cpu_up(unsigned int cpu
struct cpuhp_step *step = cpuhp_get_step(st->state);

if (!step->skip_onerr)
- cpuhp_invoke_callback(cpu, st->state, false, NULL);
+ cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
}
}

@@ -362,7 +377,7 @@ static int cpuhp_up_callbacks(unsigned i

while (st->state < target) {
st->state++;
- ret = cpuhp_invoke_callback(cpu, st->state, true, NULL);
+ ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
if (ret) {
st->target = prev_state;
undo_cpu_up(cpu, st);
@@ -428,11 +443,13 @@ static void cpuhp_thread_fun(unsigned in
if (st->cb_state < CPUHP_AP_ONLINE) {
local_irq_disable();
ret = cpuhp_invoke_callback(cpu, st->cb_state,
- st->bringup, st->node);
+ st->bringup, st->node,
+ NULL);
local_irq_enable();
} else {
ret = cpuhp_invoke_callback(cpu, st->cb_state,
- st->bringup, st->node);
+ st->bringup, st->node,
+ NULL);
}
} else if (st->rollback) {
BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);
@@ -472,7 +489,7 @@ cpuhp_invoke_ap_callback(int cpu, enum c
* we invoke the thread function directly.
*/
if (!st->thread)
- return cpuhp_invoke_callback(cpu, state, bringup, node);
+ return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);

st->cb_state = state;
st->single = true;
@@ -595,7 +612,7 @@ static int take_cpu_down(void *_param)
st->state--;
/* Invoke the former CPU_DYING callbacks */
for (; st->state > target; st->state--)
- cpuhp_invoke_callback(cpu, st->state, false, NULL);
+ cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);

/* Give up timekeeping duties */
tick_handover_do_timer();
@@ -776,7 +793,7 @@ void notify_cpu_starting(unsigned int cp
rcu_cpu_starting(cpu); /* Enables RCU usage on this CPU. */
while (st->state < target) {
st->state++;
- cpuhp_invoke_callback(cpu, st->state, true, NULL);
+ cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
}
}

@@ -1307,9 +1324,9 @@ static int cpuhp_issue_call(int cpu, enu
if (cpuhp_is_ap_state(state))
ret = cpuhp_invoke_ap_callback(cpu, state, bringup, node);
else
- ret = cpuhp_invoke_callback(cpu, state, bringup, node);
+ ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
#else
- ret = cpuhp_invoke_callback(cpu, state, bringup, node);
+ ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
#endif
BUG_ON(ret && !bringup);
return ret;

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