diff mbox series

[V4,15/37] cpu/hotplug: Rework sparse_irq locking in bringup_cpu()

Message ID 20230512205256.263722880@linutronix.de (mailing list archive)
State Handled Elsewhere
Headers show
Series [V4,01/37] x86/smpboot: Cleanup topology_phys_to_logical_pkg()/die() | expand

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conchuod/tree_selection success Guessed tree name to be for-next at HEAD ac9a78681b92
conchuod/fixes_present success Fixes tag not required for -next series
conchuod/maintainers_pattern success MAINTAINERS pattern errors before the patch: 6 and now 6
conchuod/verify_signedoff success Signed-off-by tag matches author and committer
conchuod/kdoc success Errors and warnings before: 0 this patch: 0
conchuod/build_rv64_clang_allmodconfig success Errors and warnings before: 8 this patch: 8
conchuod/module_param success Was 0 now: 0
conchuod/build_rv64_gcc_allmodconfig success Errors and warnings before: 9 this patch: 9
conchuod/build_rv32_defconfig success Build OK
conchuod/dtb_warn_rv64 success Errors and warnings before: 3 this patch: 3
conchuod/header_inline success No static functions without inline keyword in header files
conchuod/checkpatch success total: 0 errors, 0 warnings, 0 checks, 62 lines checked
conchuod/build_rv64_nommu_k210_defconfig success Build OK
conchuod/verify_fixes success No Fixes tag
conchuod/build_rv64_nommu_virt_defconfig success Build OK

Commit Message

Thomas Gleixner May 12, 2023, 9:07 p.m. UTC 
From: Thomas Gleixner <tglx@linutronix.de>

There is no harm to hold sparse_irq lock until the upcoming CPU completes
in cpuhp_online_idle(). This allows to remove cpu_online() synchronization
from architecture code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mikelley@microsoft.com>
---
V4: Amend comment about sparse irq lock - Peter Z.
---
 kernel/cpu.c |   34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)
diff mbox series

Patch

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -558,7 +558,7 @@  static int cpuhp_kick_ap(int cpu, struct
 	return ret;
 }
 
-static int bringup_wait_for_ap(unsigned int cpu)
+static int bringup_wait_for_ap_online(unsigned int cpu)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
@@ -579,15 +579,12 @@  static int bringup_wait_for_ap(unsigned
 	 */
 	if (!cpu_smt_allowed(cpu))
 		return -ECANCELED;
-
-	if (st->target <= CPUHP_AP_ONLINE_IDLE)
-		return 0;
-
-	return cpuhp_kick_ap(cpu, st, st->target);
+	return 0;
 }
 
 static int bringup_cpu(unsigned int cpu)
 {
+	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 	struct task_struct *idle = idle_thread_get(cpu);
 	int ret;
 
@@ -600,16 +597,33 @@  static int bringup_cpu(unsigned int cpu)
 	/*
 	 * Some architectures have to walk the irq descriptors to
 	 * setup the vector space for the cpu which comes online.
-	 * Prevent irq alloc/free across the bringup.
+	 *
+	 * Prevent irq alloc/free across the bringup by acquiring the
+	 * sparse irq lock. Hold it until the upcoming CPU completes the
+	 * startup in cpuhp_online_idle() which allows to avoid
+	 * intermediate synchronization points in the architecture code.
 	 */
 	irq_lock_sparse();
 
 	/* Arch-specific enabling code. */
 	ret = __cpu_up(cpu, idle);
-	irq_unlock_sparse();
 	if (ret)
-		return ret;
-	return bringup_wait_for_ap(cpu);
+		goto out_unlock;
+
+	ret = bringup_wait_for_ap_online(cpu);
+	if (ret)
+		goto out_unlock;
+
+	irq_unlock_sparse();
+
+	if (st->target <= CPUHP_AP_ONLINE_IDLE)
+		return 0;
+
+	return cpuhp_kick_ap(cpu, st, st->target);
+
+out_unlock:
+	irq_unlock_sparse();
+	return ret;
 }
 
 static int finish_cpu(unsigned int cpu)