acpi: fix bogus preemption logic
authorThomas Gleixner <tglx@linutronix.de>
Wed, 11 Aug 2010 21:17:29 +0000 (14:17 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 12 Aug 2010 15:43:29 +0000 (08:43 -0700)
The ACPI_PREEMPTION_POINT() logic was introduced in commit 8bd108d
(ACPICA: add preemption point after each opcode parse).  The follow up
commits abe1dfab6138d15692c084ca70 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>
drivers/acpi/apei/erst.c
include/acpi/platform/aclinux.h

index 864dd46c346fd33cc9c96d830d39719053c6354e..18645f4e83cdd2f22d526276b320dac631be8940 100644 (file)
@@ -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"
index e5039a2856f852b4a17d0729dd652422ed47c428..103f08aca764e23ffe81d9ee6da4fd6206e3de7b 100644 (file)
@@ -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__ */