Currently, sched_setattr mandates that a policy is always specified. Since utilization clamp attributes could apply across different scheduling policies (i.e. all but SCHED_DEADLINE), this requires also to always know which policy a task has before changing its clamp values.
This is not just cumbersome but it's also racy, indeed we cannot be sure that a task policy has been changed in between its policy read and the actual clamp value change. Sometimes however, this could be the actual use-case, we wanna change the clamps without affecting the policy. Let's fix this adding an additional attribute flag (SCHED_FLAG_TUNE_POLICY) which, when specified, will ensure to always force the usage of the current policy. This is done by re-using the SETPARAM_POLICY thing we already have for the sched_setparam syscall, thus extending its usage to the non-POSIX sched_setattr while not exposing that internal concept to user-space. Signed-off-by: Patrick Bellasi <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Suren Baghdasaryan <[email protected]> Cc: Todd Kjos <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Steve Muckle <[email protected]> Cc: Juri Lelli <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] --- Changes in v5: Message-ID: <[email protected]> - allow to change clamp values without affecting current policy --- include/uapi/linux/sched.h | 6 +++++- kernel/sched/core.c | 11 ++++++++++- 2 files changed, 15 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h index c27d6e81517b..62498d749bec 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 check attr.policy values */ +#define SCHED_POLICY_MAX 7 /* Can be ORed in to make sure the process is reverted back to SCHED_NORMAL on fork */ #define SCHED_RESET_ON_FORK 0x40000000 @@ -50,11 +52,13 @@ #define SCHED_FLAG_RESET_ON_FORK 0x01 #define SCHED_FLAG_RECLAIM 0x02 #define SCHED_FLAG_DL_OVERRUN 0x04 -#define SCHED_FLAG_UTIL_CLAMP 0x08 +#define SCHED_FLAG_TUNE_POLICY 0x08 +#define SCHED_FLAG_UTIL_CLAMP 0x10 #define SCHED_FLAG_ALL (SCHED_FLAG_RESET_ON_FORK | \ SCHED_FLAG_RECLAIM | \ SCHED_FLAG_DL_OVERRUN | \ + SCHED_FLAG_TUNE_POLICY | \ SCHED_FLAG_UTIL_CLAMP) #endif /* _UAPI_LINUX_SCHED_H */ diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3701bb1e6698..9a2e12eaa377 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4595,8 +4595,17 @@ 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 has always to be required from userspace. Unless + * the SCHED_FLAG_TUNE_POLICY is set, in which case, the current + * policy will be enforced for this call. + */ + if (attr.sched_policy >= SCHED_POLICY_MAX && + !(attr.sched_flags & SCHED_FLAG_TUNE_POLICY)) { return -EINVAL; + } + if (attr.sched_flags & SCHED_FLAG_TUNE_POLICY) + attr.sched_policy = SETPARAM_POLICY; rcu_read_lock(); retval = -ESRCH; -- 2.18.0
