acpi: fix bogus preemption logic

The ACPI_PREEMPTION_POINT() logic was introduced in commit 8bd108d
(ACPICA: add preemption point after each opcode parse).  The follow up
commits abe1dfa, 138d156, c084ca7 tried to fix the preemption logic
back and forth, but nobody noticed that the usage of
in_atomic_preempt_off() in that context is wrong.

The check which guards the call of cond_resched() is:

    if (!in_atomic_preempt_off() && !irqs_disabled())

in_atomic_preempt_off() is not intended for general use as the comment
above the macro definition clearly says:

 * Check whether we were atomic before we did preempt_disable():
 * (used by the scheduler, *after* releasing the kernel lock)

On a CONFIG_PREEMPT=n kernel the usage of in_atomic_preempt_off() works by
accident, but with CONFIG_PREEMPT=y it's just broken.

The whole purpose of the ACPI_PREEMPTION_POINT() is to reduce the latency
on a CONFIG_PREEMPT=n kernel, so make ACPI_PREEMPTION_POINT() depend on
CONFIG_PREEMPT=n and remove the in_atomic_preempt_off() check.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=16210

[[email protected]: fix build]
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Francois Valenduc <[email protected]>
Cc: Lin Ming <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

drivers/acpi/apei/erst.c

@@ -33,6 +33,7 @@
 #include <linux/uaccess.h>
 #include <linux/cper.h>
 #include <linux/nmi.h>
+#include <linux/hardirq.h>
 #include <acpi/apei.h>
 
 #include "apei-internal.h"

include/acpi/platform/aclinux.h

@@ -148,13 +148,17 @@ static inline void *acpi_os_acquire_object(acpi_cache_t * cache)
 #define ACPI_ALLOCATE_ZEROED(a) acpi_os_allocate_zeroed(a)
 #define ACPI_FREE(a)            kfree(a)
 
-/* Used within ACPICA to show where it is safe to preempt execution */
-#include <linux/hardirq.h>
+#ifndef CONFIG_PREEMPT
+/*
+ * Used within ACPICA to show where it is safe to preempt execution
+ * when CONFIG_PREEMPT=n
+ */
 #define ACPI_PREEMPTION_POINT() \
 	do { \
-		if (!in_atomic_preempt_off() && !irqs_disabled()) \
+		if (!irqs_disabled()) \
 			cond_resched(); \
 	} while (0)
+#endif
 
 #endif /* __KERNEL__ */