lkml.org 
[lkml]   [2021]   [Jun]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 2/3] sched: Skip priority checks with SCHED_FLAG_KEEP_PARAMS
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

\
 
 \ /
  Last update: 2021-06-30 18:02    [W:0.706 / U:0.184 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site