sched/core: Allow sched_setattr() to use the current policy

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@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alessio Balsini <balsini@android.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Perret <quentin.perret@arm.com>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Steve Muckle <smuckle@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Todd Kjos <tkjos@google.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lkml.kernel.org/r/20190621084217.8167-6-patrick.bellasi@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index ed4ee170bee2a5e7dc0c3cde35e1c5549799c427..58b2368d3634ee2ef8cda110a07443e8b77d29af 100644 (file)
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -51,9 +51,11 @@
 #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 b74de86b68c7fdaf3abfb9e06c125f6f5bdd624b..6d519f3f97895064a34f0f615c2f35ebd36c753e 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4897,6 +4897,8 @@ 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;