Commit bc089602 authored Jun 25, 2011 by Russell King

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>

parent df295df6

arch/arm/kernel/entry-armv.S

+16 −1

Original line number	Diff line number	Diff line
		@@ -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

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