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    Subject[ 036/135] powerpc: Update DSCR on all CPUs when writing sysfs dscr_default
    3.2-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Anton Blanchard <anton@samba.org>

    commit 1b6ca2a6fe56e7697d57348646e07df08f43b1bb upstream.

    Writing to dscr_default in sysfs doesn't actually change the DSCR -
    we rely on a context switch on each CPU to do the work. There is no
    guarantee we will get a context switch in a reasonable amount of time
    so fire off an IPI to force an immediate change.

    This issue was found with the following test case:

    http://ozlabs.org/~anton/junkcode/dscr_explicit_test.c

    Signed-off-by: Anton Blanchard <anton@samba.org>
    Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    [bwh: Backported to 3.2: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    arch/powerpc/kernel/sysfs.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    --- a/arch/powerpc/kernel/sysfs.c
    +++ b/arch/powerpc/kernel/sysfs.c
    @@ -192,6 +192,12 @@ static ssize_t show_dscr_default(struct
    return sprintf(buf, "%lx\n", dscr_default);
    }

    +static void update_dscr(void *dummy)
    +{
    + if (!current->thread.dscr_inherit)
    + mtspr(SPRN_DSCR, dscr_default);
    +}
    +
    static ssize_t __used store_dscr_default(struct sysdev_class *class,
    struct sysdev_class_attribute *attr, const char *buf,
    size_t count)
    @@ -204,6 +210,8 @@ static ssize_t __used store_dscr_default
    return -EINVAL;
    dscr_default = val;

    + on_each_cpu(update_dscr, NULL, 1);
    +
    return count;
    }




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