lkml.org 
[lkml]   [2019]   [May]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v8 05/16] sched/core: Allow sched_setattr() to use the current policy
On 08-May 21:21, Peter Zijlstra wrote:
> 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.

Looking better at the code, I see now that we don't really need that
check anymore. Indeed, v8 introduced the support to change policy
specific and independent attributes at the same time. Thus:

1. the policy validity is already checked in:

sched_setattr()
sched_setattr()
__sched_setscheduler()
valid_policy()

which knows how to deal with attr.policy=4 (i.e. -EINVAL)

2. when we pass in SCHED_FLAG_KEEP_POLICY we force the current policy
by setting attr.sched_policy = SETPARAM_POLICY, so we just need a
non negative policy being defined (usually 0 by default).

Thus, I'll remove the new #define and update the check above to be just:

if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY)
attr.sched_policy = SETPARAM_POLICY;
else if ((int)attr.sched_policy < 0)
return -EINVAL;

which should cover the additional case:

you can syscall with just SCHED_FLAG_KEEP_POLICY set if you want to
change only cross-policy attributes.

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

--
#include <best/regards.h>

Patrick Bellasi

\
 
 \ /
  Last update: 2019-05-09 16:59    [W:0.123 / U:0.312 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site