ARM: 7790/1: Fix deferred mm switch on VIVT processors

As of commit b9d4d42ad9 (ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on
pre-ARMv6 CPUs), the mm switching on VIVT processors is done in the
finish_arch_post_lock_switch() function to avoid whole cache flushing
with interrupts disabled. The need for deferred mm switch is stored as a
thread flag (TIF_SWITCH_MM). However, with preemption enabled, we can
have another thread switch before finish_arch_post_lock_switch(). If the
new thread has the same mm as the previous 'next' thread, the scheduler
will not call switch_mm() and the TIF_SWITCH_MM flag won't be set for
the new thread.

This patch moves the switch pending flag to the mm_context_t structure
since this is specific to the mm rather than thread.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Marc Kleine-Budde <mkl@pengutronix.de>
Tested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: <stable@vger.kernel.org> # 3.5+
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

3 files changed, 18 insertions, 5 deletions

diff --git a/arch/arm/include/asm/mmu.h b/arch/arm/include/asm/mmu.h
index e3d55547e755..d1b4998e4f43 100644
--- a/arch/arm/include/asm/mmu.h
+++ b/arch/arm/include/asm/mmu.h
@@ -6,6 +6,8 @@
 typedef struct {
 #ifdef CONFIG_CPU_HAS_ASID
         atomic64_t      id;
+#else
+        int             switch_pending;
 #endif
         unsigned int    vmalloc_seq;
 } mm_context_t;
diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
index b5792b7fd8d3..9b32f76bb0dd 100644
--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -56,7 +56,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
                  * on non-ASID CPUs, the old mm will remain valid until the
                  * finish_arch_post_lock_switch() call.
                  */
-                set_ti_thread_flag(task_thread_info(tsk), TIF_SWITCH_MM);
+                mm->context.switch_pending = 1;
         else
                 cpu_switch_mm(mm->pgd, mm);
 }
@@ -65,9 +65,21 @@ static inline void check_and_switch_context(struct mm_struct *mm,
         finish_arch_post_lock_switch
 static inline void finish_arch_post_lock_switch(void)
 {
-        if (test_and_clear_thread_flag(TIF_SWITCH_MM)) {
-                struct mm_struct *mm = current->mm;
-                cpu_switch_mm(mm->pgd, mm);
+        struct mm_struct *mm = current->mm;
+
+        if (mm && mm->context.switch_pending) {
+                /*
+                 * Preemption must be disabled during cpu_switch_mm() as we
+                 * have some stateful cache flush implementations. Check
+                 * switch_pending again in case we were preempted and the
+                 * switch to this mm was already done.
+                 */
+                preempt_disable();
+                if (mm->context.switch_pending) {
+                        mm->context.switch_pending = 0;
+                        cpu_switch_mm(mm->pgd, mm);
+                }
+                preempt_enable_no_resched();
         }
 }
 
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 214d4158089a..2b8114fcba09 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -156,7 +156,6 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *,
 #define TIF_USING_IWMMXT        17
 #define TIF_MEMDIE              18      /* is terminating due to OOM killer */
 #define TIF_RESTORE_SIGMASK     20
-#define TIF_SWITCH_MM           22      /* deferred switch_mm */
 
 #define _TIF_SIGPENDING         (1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED       (1 << TIF_NEED_RESCHED)