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    Subject[RFC PATCH 15/22 -v2] initialize the clock source to jiffies clock.
    The latency tracer can call clocksource_read very early in bootup and
    before the clock source variable has been initialized. This results in a
    crash at boot up (even before earlyprintk is initialized). Since the
    clock->read variable points to NULL.

    This patch simply initializes the clock to use clocksource_jiffies, so
    that any early user of clocksource_read will not crash.

    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    Acked-by: John Stultz <johnstul@us.ibm.com>
    ---
    include/linux/clocksource.h | 3 +++
    kernel/time/timekeeping.c | 9 +++++++--
    2 files changed, 10 insertions(+), 2 deletions(-)
    Index: linux-compile-i386.git/kernel/time/timekeeping.c
    ===================================================================
    --- linux-compile-i386.git.orig/kernel/time/timekeeping.c 2008-01-09 14:17:53.000000000 -0500
    +++ linux-compile-i386.git/kernel/time/timekeeping.c 2008-01-09 15:17:30.000000000 -0500
    @@ -53,8 +53,13 @@ static inline void update_xtime_cache(u6
    timespec_add_ns(&xtime_cache, nsec);
    }

    -static struct clocksource *clock; /* pointer to current clocksource */
    -
    +/*
    + * pointer to current clocksource
    + * Just in case we use clocksource_read before we initialize
    + * the actual clock source. Instead of calling a NULL read pointer
    + * we return jiffies.
    + */
    +static struct clocksource *clock = &clocksource_jiffies;

    #ifdef CONFIG_GENERIC_TIME
    /**
    Index: linux-compile-i386.git/include/linux/clocksource.h
    ===================================================================
    --- linux-compile-i386.git.orig/include/linux/clocksource.h 2008-01-09 14:23:42.000000000 -0500
    +++ linux-compile-i386.git/include/linux/clocksource.h 2008-01-09 15:17:30.000000000 -0500
    @@ -274,6 +274,9 @@ extern struct clocksource* clocksource_g
    extern void clocksource_change_rating(struct clocksource *cs, int rating);
    extern void clocksource_resume(void);

    +/* used to initialize clock */
    +extern struct clocksource clocksource_jiffies;
    +
    #ifdef CONFIG_GENERIC_TIME_VSYSCALL
    extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
    extern void update_vsyscall_tz(void);
    --


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