[PATCH 3/3] ARM: vfp: Use vfp_lock() in vfp_entry().

[Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>]

vfp_entry() is invoked from exception handler and is fully preemptible.
It uses local_bh_disable() to remain uninterrupted while checking the
VFP state.
This is not working on PREEMPT_RT because local_bh_disable()
synchronizes the relevant section but the context remains fully
preemptible.

Use vfp_lock() for uninterrupted access.

VFP_bounce() is invoked from within vfp_entry() and may send a signal.
Sending a signal uses spinlock_t which becomes a sleeping lock
on PREEMPT_RT and must not be acquired within a preempt-disabled
section. Move the vfp_raise_sigfpe() block outside of the
preempt-disabled section.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 arch/arm/vfp/vfphw.S     |  7 ++-----
 arch/arm/vfp/vfpmodule.c | 30 ++++++++++++++++++++----------
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index a4610d0f32152..860512042bc21 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -180,10 +180,7 @@ ENTRY(vfp_support_entry)
 					@ always subtract 4 from the following
 					@ instruction address.
 
-local_bh_enable_and_ret:
-	adr	r0, .
-	mov	r1, #SOFTIRQ_DISABLE_OFFSET
-	b	__local_bh_enable_ip	@ tail call
+	b	vfp_exit	@ tail call
 
 look_for_VFP_exceptions:
 	@ Check for synchronous or asynchronous exception
@@ -206,7 +203,7 @@ ENTRY(vfp_support_entry)
 	@ not recognised by VFP
 
 	DBGSTR	"not VFP"
-	b	local_bh_enable_and_ret
+	b	vfp_exit	@ tail call
 
 process_exception:
 	DBGSTR	"bounce"
diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 543dc7f5a27e3..a2745d17e9c71 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -267,7 +267,7 @@ static void vfp_panic(char *reason, u32 inst)
 /*
  * Process bitmask of exception conditions.
  */
-static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_regs *regs)
+static int vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr)
 {
 	int si_code = 0;
 
@@ -275,8 +275,7 @@ static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_
 
 	if (exceptions == VFP_EXCEPTION_ERROR) {
 		vfp_panic("unhandled bounce", inst);
-		vfp_raise_sigfpe(FPE_FLTINV, regs);
-		return;
+		return FPE_FLTINV;
 	}
 
 	/*
@@ -304,8 +303,7 @@ static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_
 	RAISE(FPSCR_OFC, FPSCR_OFE, FPE_FLTOVF);
 	RAISE(FPSCR_IOC, FPSCR_IOE, FPE_FLTINV);
 
-	if (si_code)
-		vfp_raise_sigfpe(si_code, regs);
+	return si_code;
 }
 
 /*
@@ -350,6 +348,8 @@ static u32 vfp_emulate_instruction(u32 inst, u32 fpscr, struct pt_regs *regs)
 void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 {
 	u32 fpscr, orig_fpscr, fpsid, exceptions;
+	int si_code2 = 0;
+	int si_code = 0;
 
 	pr_debug("VFP: bounce: trigger %08x fpexc %08x\n", trigger, fpexc);
 
@@ -397,7 +397,7 @@ void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 		 * unallocated VFP instruction but with FPSCR.IXE set and not
 		 * on VFP subarch 1.
 		 */
-		 vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr, regs);
+		si_code = vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr);
 		goto exit;
 	}
 
@@ -422,7 +422,7 @@ void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 	 */
 	exceptions = vfp_emulate_instruction(trigger, fpscr, regs);
 	if (exceptions)
-		vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);
+		si_code2 = vfp_raise_exceptions(exceptions, trigger, orig_fpscr);
 
 	/*
 	 * If there isn't a second FP instruction, exit now. Note that
@@ -441,9 +441,14 @@ void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
  emulate:
 	exceptions = vfp_emulate_instruction(trigger, orig_fpscr, regs);
 	if (exceptions)
-		vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);
+		si_code = vfp_raise_exceptions(exceptions, trigger, orig_fpscr);
+
  exit:
-	local_bh_enable();
+	vfp_unlock();
+	if (si_code2)
+		vfp_raise_sigfpe(si_code2, regs);
+	if (si_code)
+		vfp_raise_sigfpe(si_code, regs);
 }
 
 static void vfp_enable(void *unused)
@@ -684,10 +689,15 @@ asmlinkage void vfp_entry(u32 trigger, struct thread_info *ti, u32 resume_pc,
 	if (unlikely(!have_vfp))
 		return;
 
-	local_bh_disable();
+	vfp_lock();
 	vfp_support_entry(trigger, ti, resume_pc, resume_return_address);
 }
 
+asmlinkage void vfp_exit(void)
+{
+	vfp_unlock();
+}
+
 #ifdef CONFIG_KERNEL_MODE_NEON
 
 static int vfp_kmode_exception(struct pt_regs *regs, unsigned int instr)
-- 
2.40.1