Subject: [PATCH] arm64/sve: Delay freeing memory in fpsimd_flush_thread()
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Thu, 29 Jul 2021 12:52:14 +0200

fpsimd_flush_thread() invokes kfree() via sve_free() within a preempt disabled
section which is not working on -RT.

Delay freeing of memory until preemption is enabled again.

Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 arch/arm64/kernel/fpsimd.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1033,6 +1033,7 @@ void fpsimd_thread_switch(struct task_st
 void fpsimd_flush_thread(void)
 {
 	int vl, supported_vl;
+	void *sve_state = NULL;
 
 	if (!system_supports_fpsimd())
 		return;
@@ -1045,7 +1046,10 @@ void fpsimd_flush_thread(void)
 
 	if (system_supports_sve()) {
 		clear_thread_flag(TIF_SVE);
-		sve_free(current);
+
+		/* Defer kfree() while in atomic context */
+		sve_state = current->thread.sve_state;
+		current->thread.sve_state = NULL;
 
 		/*
 		 * Reset the task vector length as required.
@@ -1079,6 +1083,7 @@ void fpsimd_flush_thread(void)
 	}
 
 	put_cpu_fpsimd_context();
+	kfree(sve_state);
 }
 
 /*