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 <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> --- Changes in v9: Message-ID: <20190509145901.um7rrsslg7de4blf@e110439-lin> - get rid of not necessary SCHED_POLICY_MAX define - update sched_setattr() syscall to just force the current policy on SCHED_FLAG_KEEP_POLICY --- include/uapi/linux/sched.h | 4 +++- kernel/sched/core.c | 2 ++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h index 22627f80063e..261b6e43846c 100644 --- a/include/uapi/linux/sched.h +++ b/include/uapi/linux/sched.h @@ -50,9 +50,11 @@ #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 dac73a5959b6..43b29b2efa4c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4863,6 +4863,8 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr, if ((int)attr.sched_policy < 0) return -EINVAL; + if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY) + attr.sched_policy = SETPARAM_POLICY; rcu_read_lock(); retval = -ESRCH; -- 2.21.0
