ARM: 7627/1: Predicate preempt logic on PREEMP_COUNT not PREEMPT alone

commit 568dca15 upstream.

Patrik Kluba reports that the preempt count becomes invalid due
to the preempt_enable() call being unbalanced with a
preempt_disable() call in the vfp assembly routines. This happens
because preempt_enable() and preempt_disable() update preempt
counts under PREEMPT_COUNT=y but the vfp assembly routines do so
under PREEMPT=y. In a configuration where PREEMPT=n and
DEBUG_ATOMIC_SLEEP=y, PREEMPT_COUNT=y and so the preempt_enable()
call in VFP_bounce() keeps subtracting from the preempt count
until it goes negative.

Fix this by always using PREEMPT_COUNT to decided when to update
preempt counts in the ARM assembly code.
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Reported-by: Patrik Kluba <pkluba@dension.com>
Tested-by: Patrik Kluba <pkluba@dension.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm/vfp/entry.S

@@ -22,7 +22,7 @@
 @  IRQs disabled.
 @
 ENTRY(do_vfp)
-#ifdef CONFIG_PREEMPT
+#ifdef CONFIG_PREEMPT_COUNT
 	ldr	r4, [r10, #TI_PREEMPT]	@ get preempt count
 	add	r11, r4, #1		@ increment it
 	str	r11, [r10, #TI_PREEMPT]
@@ -35,7 +35,7 @@ ENTRY(do_vfp)
 ENDPROC(do_vfp)
 
 ENTRY(vfp_null_entry)
-#ifdef CONFIG_PREEMPT
+#ifdef CONFIG_PREEMPT_COUNT
 	get_thread_info	r10
 	ldr	r4, [r10, #TI_PREEMPT]	@ get preempt count
 	sub	r11, r4, #1		@ decrement it
@@ -53,7 +53,7 @@ ENDPROC(vfp_null_entry)
 
 	__INIT
 ENTRY(vfp_testing_entry)
-#ifdef CONFIG_PREEMPT
+#ifdef CONFIG_PREEMPT_COUNT
 	get_thread_info	r10
 	ldr	r4, [r10, #TI_PREEMPT]	@ get preempt count
 	sub	r11, r4, #1		@ decrement it

arch/arm/vfp/vfphw.S

@@ -167,7 +167,7 @@ vfp_hw_state_valid:
 					@ else it's one 32-bit instruction, so
 					@ always subtract 4 from the following
 					@ instruction address.
-#ifdef CONFIG_PREEMPT
+#ifdef CONFIG_PREEMPT_COUNT
 	get_thread_info	r10
 	ldr	r4, [r10, #TI_PREEMPT]	@ get preempt count
 	sub	r11, r4, #1		@ decrement it
@@ -191,7 +191,7 @@ look_for_VFP_exceptions:
 	@ not recognised by VFP
 
 	DBGSTR	"not VFP"
-#ifdef CONFIG_PREEMPT
+#ifdef CONFIG_PREEMPT_COUNT
 	get_thread_info	r10
 	ldr	r4, [r10, #TI_PREEMPT]	@ get preempt count
 	sub	r11, r4, #1		@ decrement it