Subject: [PATCH 2/4] ARM: vfp: Use vfp_state_hold() in vfp_sync_hwstate().
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Mon, 1 Jul 2024 12:56:54 +0200

vfp_sync_hwstate() uses preempt_disable() followed by local_bh_disable()
to ensure that it won't get interrupted while checking the VFP state.
This harms PREEMPT_RT because softirq handling can get preempted and
local_bh_disable() synchronizes the related section with a sleeping lock
which does not work with disabled preemption.

Use the vfp_state_hold() to synchronize the access.

Reviewed-by: Ard Biesheuvel <[email-masked]>
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 arch/arm/vfp/vfpmodule.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -540,11 +540,9 @@ static inline void vfp_pm_init(void) { }
  */
 void vfp_sync_hwstate(struct thread_info *thread)
 {
-	unsigned int cpu = get_cpu();
+	vfp_state_hold();
 
-	local_bh_disable();
-
-	if (vfp_state_in_hw(cpu, thread)) {
+	if (vfp_state_in_hw(raw_smp_processor_id(), thread)) {
 		u32 fpexc = fmrx(FPEXC);
 
 		/*
@@ -555,8 +553,7 @@ void vfp_sync_hwstate(struct thread_info
 		fmxr(FPEXC, fpexc);
 	}
 
-	local_bh_enable();
-	put_cpu();
+	vfp_state_release();
 }
 
 /* Ensure that the thread reloads the hardware VFP state on the next use. */