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>

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 920dd3d0795740e78e3650a651ab06afaf4fa2b9..f863ee79093ee0adc88835d5c214a60ef35f1de3 100644 (file)
--- 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