On Fri, 11 May 2007 00:36:25 +0200
"Rafael J. Wysocki" <[email protected]> wrote:
> The reading of PF_BORROWED_MM in is_user_space() without task_lock() is racy.
> Fix it.
>
> Signed-off-by: Rafael J. Wysocki <[email protected]>
> Acked-by: Pavel Machek <[email protected]>
> ---
> kernel/power/process.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/kernel/power/process.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/process.c 2007-05-10 21:44:23.000000000 +0200
> +++ linux-2.6/kernel/power/process.c 2007-05-10 21:44:28.000000000 +0200
> @@ -8,6 +8,7 @@
>
> #undef DEBUG
>
> +#include <linux/sched.h>
> #include <linux/interrupt.h>
> #include <linux/suspend.h>
> #include <linux/module.h>
> @@ -88,7 +89,12 @@ 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;
> }
The whole function is racy, isn't it? I mean, the condition which it is
testing can go from true->false or false->true at any instant after this
function returns its now-wrong value.
iow, callers of this function need to to something to prevent the expression
`p->mm && !(p->flags & PF_BORROWED_MM);' from changing value _anyway_. In
which case the new locking is not needed?
-
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