The sched_setattr() syscall mandates that a policy is always specified. This requires to always know which policy a task will have when attributes are configured and this makes it impossible to add more generic task attributes valid across different scheduling policies. Reading the policy before setting generic tasks attributes is racy since we cannot be sure it is not changed concurrently. Introduce the required support to change generic task attributes without affecting the current task policy. This is done by adding an attribute flag (SCHED_FLAG_KEEP_POLICY) to enforce the usage of the current policy. Add support for the SETPARAM_POLICY policy, which is already used by the sched_setparam() POSIX syscall, to the sched_setattr() non-POSIX syscall. Signed-off-by: Patrick Bellasi <patrick.bellasi@xxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> --- 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 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 /* 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; + } + if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY) + attr.sched_policy = SETPARAM_POLICY; rcu_read_lock(); retval = -ESRCH; -- 2.20.1