ARM: entry: instrument usr exception handlers with irqsoff tracing

As we no longer re-enable interrupts in these exception handlers, add
the irqsoff tracing calls to them so that the kernel tracks the state
more accurately.

Note that these calls are conditional on IRQSOFF_TRACER:

  kernel ----------> user ---------> kernel
          ^ irqs enabled   ^ irqs disabled

No kernel code can run on the local CPU until we've re-entered the
kernel through one of the exception handlers - and userspace can not
take any locks etc.  So, the kernel doesn't care about the IRQ mask
state while userspace is running unless we're doing IRQ off latency
tracing.  So, we can (and do) avoid the overhead of updating the IRQ
mask state on every kernel->user and user->kernel transition.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 16 insertions, 1 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 920dd3d07957..f863ee79093e 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -421,6 +421,11 @@ ENDPROC(__pabt_svc)
         .align  5
 __dabt_usr:
         usr_entry
+
+#ifdef CONFIG_IRQSOFF_TRACER
+        bl      trace_hardirqs_off
+#endif
+
         kuser_cmpxchg_check
         dabt_helper
 
@@ -433,12 +438,12 @@ ENDPROC(__dabt_usr)
         .align  5
 __irq_usr:
         usr_entry
-        kuser_cmpxchg_check
 
 #ifdef CONFIG_IRQSOFF_TRACER
         bl      trace_hardirqs_off
 #endif
 
+        kuser_cmpxchg_check
         irq_handler
         get_thread_info tsk
         mov     why, #0
@@ -451,6 +456,11 @@ ENDPROC(__irq_usr)
         .align  5
 __und_usr:
         usr_entry
+
+#ifdef CONFIG_IRQSOFF_TRACER
+        bl      trace_hardirqs_off
+#endif
+
         mov     r2, r4
         mov     r3, r5
 
@@ -669,6 +679,11 @@ ENDPROC(__und_usr_unknown)
         .align  5
 __pabt_usr:
         usr_entry
+
+#ifdef CONFIG_IRQSOFF_TRACER
+        bl      trace_hardirqs_off
+#endif
+
         pabt_helper
         mov     r2, sp                          @ regs
         bl      do_PrefetchAbort                @ call abort handler