[tip: smp/core] cpu/hotplug: Add debug printks for hotplug callback failures

[tip-bot2 for Dongli Zhang]

The following commit has been merged into the smp/core branch of tip:

Commit-ID:     ebca71a8c96f0af2ba482489ecc64d88979cd825
Gitweb:        https://git.kernel.org/tip/ebca71a8c96f0af2ba482489ecc64d88979cd825
Author:        Dongli Zhang <dongli.zhang@xxxxxxxxxx>
AuthorDate:    Thu, 08 Apr 2021 22:53:16 -07:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Tue, 10 Aug 2021 18:31:32 +02:00

cpu/hotplug: Add debug printks for hotplug callback failures

CPU hotplug callbacks can fail and cause a rollback to the previous
state. These failures are silent and therefore hard to debug.

Add pr_debug() to the up and down paths which provide information about the
error code, the CPU and the failed state. The debug printks can be enabled
via kernel command line or sysfs.

[ tglx: Adopt to current mainline, massage printk and changelog ]

Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Qais Yousef <qais.yousef@xxxxxxx>
Link: https://lore.kernel.org/r/20210409055316.1709-1-dongli.zhang@xxxxxxxxxx

---
 kernel/cpu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 7ef28e1..192e43a 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -692,6 +692,10 @@ static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
 
 	ret = cpuhp_invoke_callback_range(true, cpu, st, target);
 	if (ret) {
+		pr_debug("CPU UP failed (%d) CPU %u state %s (%d)\n",
+			 ret, cpu, cpuhp_get_step(st->state)->name,
+			 st->state);
+
 		cpuhp_reset_state(st, prev_state);
 		if (can_rollback_cpu(st))
 			WARN_ON(cpuhp_invoke_callback_range(false, cpu, st,
@@ -1091,6 +1095,9 @@ static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
 
 	ret = cpuhp_invoke_callback_range(false, cpu, st, target);
 	if (ret) {
+		pr_debug("CPU DOWN failed (%d) CPU %u state %s (%d)\n",
+			 ret, cpu, cpuhp_get_step(st->state)->name,
+			 st->state);
 
 		cpuhp_reset_state(st, prev_state);