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SubjectRe: [PATCH v8 05/16] sched/core: Allow sched_setattr() to use the current policy
On Tue, Apr 02, 2019 at 11:41:41AM +0100, Patrick Bellasi wrote:
> diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
> index 22627f80063e..075c610adf45 100644
> --- a/include/uapi/linux/sched.h
> +++ b/include/uapi/linux/sched.h
> @@ -40,6 +40,8 @@
> /* SCHED_ISO: reserved but not implemented yet */
> #define SCHED_IDLE 5
> #define SCHED_DEADLINE 6
> +/* Must be the last entry: used to sanity check attr.policy values */
> +#define SCHED_POLICY_MAX SCHED_DEADLINE

This is a wee bit sad to put in a uapi header; but yeah, where else :/

Another option would be something like:

enum {
SCHED_NORMAL = 0,
SCHED_FIFO = 1,
SCHED_RR = 2,
SCHED_BATCH = 3,
/* SCHED_ISO = 4, reserved */
SCHED_IDLE = 5,
SCHED_DEADLINE = 6,
SCHED_POLICY_NR
};

> /* Can be ORed in to make sure the process is reverted back to SCHED_NORMAL on fork */
> #define SCHED_RESET_ON_FORK 0x40000000
> @@ -50,9 +52,11 @@
> #define SCHED_FLAG_RESET_ON_FORK 0x01
> #define SCHED_FLAG_RECLAIM 0x02
> #define SCHED_FLAG_DL_OVERRUN 0x04
> +#define SCHED_FLAG_KEEP_POLICY 0x08
>
> #define SCHED_FLAG_ALL (SCHED_FLAG_RESET_ON_FORK | \
> SCHED_FLAG_RECLAIM | \
> - SCHED_FLAG_DL_OVERRUN)
> + SCHED_FLAG_DL_OVERRUN | \
> + SCHED_FLAG_KEEP_POLICY)
>
> #endif /* _UAPI_LINUX_SCHED_H */
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index d368ac26b8aa..20efb32e1a7e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4907,8 +4907,17 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
> if (retval)
> return retval;
>
> - if ((int)attr.sched_policy < 0)
> + /*
> + * A valid policy is always required from userspace, unless
> + * SCHED_FLAG_KEEP_POLICY is set and the current policy
> + * is enforced for this call.
> + */
> + if (attr.sched_policy > SCHED_POLICY_MAX &&
> + !(attr.sched_flags & SCHED_FLAG_KEEP_POLICY)) {
> return -EINVAL;
> + }

And given I just looked at those darn SCHED_* things, I now note the
above does 'funny' things when passed: attr.policy=4.

> + if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY)
> + attr.sched_policy = SETPARAM_POLICY;
>
> rcu_read_lock();
> retval = -ESRCH;

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