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    Subject[003/114] acpi: fix bogus preemption logic
    2.6.35-stable review patch.  If anyone has any objections, please let us know.


    From: Thomas Gleixner <>

    commit 0a7992c90828a65281c3c9cf180be3b432d277b2 upstream.

    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.


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

    drivers/acpi/apei/erst.c | 1 +
    include/acpi/platform/aclinux.h | 10 +++++++---
    2 files changed, 8 insertions(+), 3 deletions(-)

    --- 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"
    --- a/include/acpi/platform/aclinux.h
    +++ b/include/acpi/platform/aclinux.h
    @@ -148,13 +148,17 @@ static inline void *acpi_os_acquire_obje
    #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
    + */
    do { \
    - if (!in_atomic_preempt_off() && !irqs_disabled()) \
    + if (!irqs_disabled()) \
    cond_resched(); \
    } while (0)

    #endif /* __KERNEL__ */

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      Last update: 2010-08-25 01:27    [W:0.021 / U:46.588 seconds]
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