2015-11-25 18:02 GMT+03:00 Peter Zijlstra <peterz@xxxxxxxxxxxxx>:
> On Wed, Nov 25, 2015 at 03:43:54PM +0100, Peter Zijlstra wrote:
>> On Mon, Sep 21, 2015 at 04:01:41PM -0400, Tejun Heo wrote:
>> > So, the only way the patch could have caused the above is if someone
>> > who isn't the task itself is writing to the bitfields while the task
>> > is running. Looking through the fields, ->sched_reset_on_fork seems a
>> > bit suspicious. __sched_setscheduler() looks like it can modify the
>> > bit while the target task is running. Peter, am I misreading the
>> > code?
>>
>> Nope, that's quite possible. Looks like we need to break up those
>> bitfields a bit. All the scheduler ones should be serialized by
>> scheduler locks, but the others are fair game.
>
> Maybe something like so; but my brain is a complete mess today.
>
> ---
> include/linux/sched.h | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index f425aac63317..b474e0f05327 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1455,14 +1455,15 @@ struct task_struct {
> /* Used for emulating ABI behavior of previous Linux versions */
> unsigned int personality;
>
> - unsigned in_execve:1; /* Tell the LSMs that the process is doing an
> - * execve */
> - unsigned in_iowait:1;
> -
> - /* Revert to default priority/policy when forking */
> + /* scheduler bits, serialized by scheduler locks */
> unsigned sched_reset_on_fork:1;
> unsigned sched_contributes_to_load:1;
> unsigned sched_migrated:1;
> + unsigned __padding_sched:29;
AFAIK the order of bit fields is implementation defined, so GCC could
sort all these bits as it wants.
You could use unnamed zero-widht bit-field to force padding:
unsigned :0; //force aligment to the next boundary.
> +
> + /* unserialized, strictly 'current' */
> + unsigned in_execve:1; /* bit to tell LSMs we're in execve */
> + unsigned in_iowait:1;
> #ifdef CONFIG_MEMCG
> unsigned memcg_may_oom:1;
> #endif
>
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