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 abe1dfab6, 138d15692, c084ca70 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

[akpm@linux-foundation.org: fix build]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Len Brown <lenb@kernel.org>
Cc: Francois Valenduc <francois.valenduc@tvcablenet.be>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/acpi/apei/erst.c b/drivers/acpi/apei/erst.c
index 864dd46c346fd33cc9c96d830d39719053c6354e..18645f4e83cdd2f22d526276b320dac631be8940 100644 (file)
--- a/drivers/acpi/apei/erst.c
+++ b/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"

diff --git a/include/acpi/platform/aclinux.h b/include/acpi/platform/aclinux.h
index e5039a2856f852b4a17d0729dd652422ed47c428..103f08aca764e23ffe81d9ee6da4fd6206e3de7b 100644 (file)
--- a/include/acpi/platform/aclinux.h
+++ b/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__ */