Messages in this thread | | | Date | Wed, 30 Jun 2021 17:01:56 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH v3 2/3] sched: Skip priority checks with SCHED_FLAG_KEEP_PARAMS |
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On 06/23/21 12:34, Quentin Perret wrote: > SCHED_FLAG_KEEP_PARAMS can be passed to sched_setattr to specify that > the call must not touch scheduling parameters (nice or priority). This > is particularly handy for uclamp when used in conjunction with > SCHED_FLAG_KEEP_POLICY as that allows to issue a syscall that only > impacts uclamp values. > > However, sched_setattr always checks whether the priorities and nice > values passed in sched_attr are valid first, even if those never get > used down the line. This is useless at best since userspace can > trivially bypass this check to set the uclamp values by specifying low > priorities. However, it is cumbersome to do so as there is no single > expression of this that skips both RT and CFS checks at once. As such, > userspace needs to query the task policy first with e.g. sched_getattr > and then set sched_attr.sched_priority accordingly. This is racy and > slower than a single call. > > As the priority and nice checks are useless when SCHED_FLAG_KEEP_PARAMS > is specified, simply inherit them in this case to match the policy > inheritance of SCHED_FLAG_KEEP_POLICY. > > Reported-by: Wei Wang <wvw@google.com> > Signed-off-by: Quentin Perret <qperret@google.com> > ---
LGTM.
Reviewed-by: Qais Yousef <qais.yousef@arm.com>
Cheers
-- Qais Yousef
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