[RFT PATCH] ARM: vfp: Fix broken softirq handling with instrumentation enabled

[Ard Biesheuvel]

Commit 62b95a7b44d1 (ARM: 9282/1: vfp: Manipulate task VFP state with
softirqs disabled) replaced the en/disable preemption calls inside the
VFP state handling code with en/disabling of soft IRQs, which is
necessary to allow kernel use of the VFP/SIMD unit when handling a soft
IRQ.

Unfortunately, when lockdep is enabled (or other instrumentation that
enables TRACE_IRQFLAGS), the disable path implemented in asm fails to
perform the lockdep and RCU related bookkeeping, resulting in spurious
warnings and other badness.

So let's call the C versions when they are available, and only fall back
to direct manipulation of the preempt_count when we disable soft IRQs
with those instrumentations disabled.

Cc: Frederic Weisbecker <frederic at kernel.org>
Cc: Guenter Roeck <linux at roeck-us.net>
Cc: Peter Zijlstra <peterz at infradead.org>
Link: https://lore.kernel.org/all/ZBBYCSZUJOWBg1s8@localhost.localdomain/
Fixes: 62b95a7b44d1 (ARM: 9282/1: vfp: Manipulate task VFP state with softirqs disabled)
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm/include/asm/assembler.h | 15 ++++----------
 arch/arm/vfp/entry.S             | 21 +++++++++++++++++---
 arch/arm/vfp/vfphw.S             |  8 ++++----
 3 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 06b48ce23e1ca245..d9f7c546781a39eb 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -244,17 +244,10 @@ THUMB(	fpreg	.req	r7	)
 	.endm
 #endif
 
-	.macro	local_bh_disable, ti, tmp
-	ldr	\tmp, [\ti, #TI_PREEMPT]
-	add	\tmp, \tmp, #SOFTIRQ_DISABLE_OFFSET
-	str	\tmp, [\ti, #TI_PREEMPT]
-	.endm
-
-	.macro	local_bh_enable_ti, ti, tmp
-	get_thread_info \ti
-	ldr	\tmp, [\ti, #TI_PREEMPT]
-	sub	\tmp, \tmp, #SOFTIRQ_DISABLE_OFFSET
-	str	\tmp, [\ti, #TI_PREEMPT]
+	.macro	local_bh_enable_and_ret
+	adr	r0, .
+	mov	r1, #SOFTIRQ_DISABLE_OFFSET
+	b	__local_bh_enable_ip
 	.endm
 
 #define USERL(l, x...)				\
diff --git a/arch/arm/vfp/entry.S b/arch/arm/vfp/entry.S
index 9a89264cdcc0b46e..9555c0a1c46fd47b 100644
--- a/arch/arm/vfp/entry.S
+++ b/arch/arm/vfp/entry.S
@@ -22,7 +22,23 @@
 @  IRQs enabled.
 @
 ENTRY(do_vfp)
-	local_bh_disable r10, r4
+#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_TRACE_IRQFLAGS)
+	mov	r4, r0			@ stash r0, r2, lr
+	mov	r5, r2
+	mov	r6, lr
+
+	adr	r0, .
+	mov	r1, #SOFTIRQ_DISABLE_OFFSET
+	bl	__local_bh_disable_ip
+
+	mov	r0, r4			@ restore r0, r2, lr
+	mov	r2, r5
+	mov	lr, r6
+#else
+	ldr	r4, [r10, #TI_PREEMPT]
+	add	r4, r4, #SOFTIRQ_DISABLE_OFFSET
+	str	r4, [r10, #TI_PREEMPT]
+#endif
  	ldr	r4, .LCvfp
 	ldr	r11, [r10, #TI_CPU]	@ CPU number
 	add	r10, r10, #TI_VFPSTATE	@ r10 = workspace
@@ -30,8 +46,7 @@ ENTRY(do_vfp)
 ENDPROC(do_vfp)
 
 ENTRY(vfp_null_entry)
-	local_bh_enable_ti r10, r4
-	ret	lr
+	local_bh_enable_and_ret		@ tail call
 ENDPROC(vfp_null_entry)
 
 	.align	2
diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index 26c4f61ecfa39638..84523de8bf059ce8 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -175,8 +175,9 @@ vfp_hw_state_valid:
 					@ else it's one 32-bit instruction, so
 					@ always subtract 4 from the following
 					@ instruction address.
-	local_bh_enable_ti r10, r4
-	ret	r9			@ we think we have handled things
+
+	mov	lr, r9			@ we think we have handled things
+	local_bh_enable_and_ret		@ tail call
 
 
 look_for_VFP_exceptions:
@@ -200,8 +201,7 @@ skip:
 	@ not recognised by VFP
 
 	DBGSTR	"not VFP"
-	local_bh_enable_ti r10, r4
-	ret	lr
+	local_bh_enable_and_ret		@ tail call
 
 process_exception:
 	DBGSTR	"bounce"
-- 
2.39.2