MIPS: Make local_irq_disable macro safe for non-Mipsr2

For non-mipsr2 processors, the local_irq_disable contains an mfc0-mtc0
pair with instructions inbetween.  With preemption enabled, this sequence
may get preempted and effect a stale value of CP0_STATUS when executing
the mtc0 instruction.  This commit avoids this scenario by incrementing
the preempt count before the mfc0 and decrementing it after the mtc9.

[ralf@linux-mips.org: This patch is sorting out the part that were missed
by e97c5b6098 [MIPS: Make irqflags.h functions preempt-safe for non-mipsr2
cpus.]  I also re-enabled the inclusion of <asm/asm-offsets.h> at the top
of <asm/asmmacro.h>].

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: cernekee@gmail.com
Patchwork: https://patchwork.linux-mips.org/patch/6164/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/mips/include/asm/asmmacro.h b/arch/mips/include/asm/asmmacro.h
index 69a9a22d014a..4225e99bd7bf 100644
--- a/arch/mips/include/asm/asmmacro.h
+++ b/arch/mips/include/asm/asmmacro.h
@@ -9,6 +9,7 @@
 #define _ASM_ASMMACRO_H
 
 #include <asm/hazards.h>
+#include <asm/asm-offsets.h>
 
 #ifdef CONFIG_32BIT
 #include <asm/asmmacro-32.h>
@@ -54,11 +55,21 @@
         .endm
 
         .macro  local_irq_disable reg=t0
+#ifdef CONFIG_PREEMPT
+        lw      \reg, TI_PRE_COUNT($28)
+        addi    \reg, \reg, 1
+        sw      \reg, TI_PRE_COUNT($28)
+#endif
         mfc0    \reg, CP0_STATUS
         ori     \reg, \reg, 1
         xori    \reg, \reg, 1
         mtc0    \reg, CP0_STATUS
         irq_disable_hazard
+#ifdef CONFIG_PREEMPT
+        lw      \reg, TI_PRE_COUNT($28)
+        addi    \reg, \reg, -1
+        sw      \reg, TI_PRE_COUNT($28)
+#endif
         .endm
 #endif /* CONFIG_MIPS_MT_SMTC */