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Subject[ 057/128] ARM: 7627/1: Predicate preempt logic on PREEMP_COUNT not PREEMPT alone
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stephen Boyd <sboyd@codeaurora.org>

commit 568dca15aa2a0f4ddee255894ec393a159f13147 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: Ben Hutchings <ben@decadent.org.uk>
---
arch/arm/vfp/entry.S | 6 +++---
arch/arm/vfp/vfphw.S | 4 ++--
2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/arm/vfp/entry.S b/arch/arm/vfp/entry.S
index cc926c9..323ce1a 100644
--- a/arch/arm/vfp/entry.S
+++ b/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
diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index ea0349f..dd5e56f 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -168,7 +168,7 @@ 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
@@ -192,7 +192,7 @@ 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



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