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    Subject[PATCH -mm 1/7] Freezer: Read PF_BORROWED_MM in a nonracy way
    Date
    From: Rafael J. Wysocki <rjw@sisk.pl>

    The reading of PF_BORROWED_MM in is_user_space() without task_lock() is racy.
    Fix it.

    Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
    Acked-by: Pavel Machek <pavel@ucw.cz>
    ---
    kernel/power/process.c | 8 +++++++-
    1 file changed, 7 insertions(+), 1 deletion(-)

    Index: linux-2.6.20-mm2/kernel/power/process.c
    ===================================================================
    --- linux-2.6.20-mm2.orig/kernel/power/process.c 2007-02-25 14:02:55.000000000 +0100
    +++ linux-2.6.20-mm2/kernel/power/process.c 2007-02-25 14:03:51.000000000 +0100
    @@ -8,6 +8,7 @@

    #undef DEBUG

    +#include <linux/sched.h>
    #include <linux/smp_lock.h>
    #include <linux/interrupt.h>
    #include <linux/suspend.h>
    @@ -87,7 +88,12 @@ static void cancel_freezing(struct task_

    static inline int is_user_space(struct task_struct *p)
    {
    - return p->mm && !(p->flags & PF_BORROWED_MM);
    + int ret;
    +
    + task_lock(p);
    + ret = p->mm && !(p->flags & PF_BORROWED_MM);
    + task_unlock(p);
    + return ret;
    }

    static unsigned int try_to_freeze_tasks(int freeze_user_space)
    -
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