Messages in this thread | | | Subject | Re: [PATCH 1/2] sched/deadline: Fix reset_on_fork reporting of DL tasks | From | Dietmar Eggemann <> | Date | Thu, 29 Jul 2021 18:26:40 +0200 |
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On 27/07/2021 12:11, Quentin Perret wrote: > It is possible for sched_getattr() to incorrectly report the state of > the reset_on_fork flag when called on a deadline task. > > Indeed, if the flag was set on a deadline task using sched_setattr() > with flags (SCHED_FLAG_RESET_ON_FORK | SCHED_FLAG_KEEP_PARAMS), then > p->sched_reset_on_fork will be set, but __setscheduler() will bail out > early, which means that the dl_se->flags will not get updated by > __setscheduler_params()->__setparam_dl(). Consequently, if
True, but it would also be awkward if non-DL related flags would have to be stored in dl_se->flags.
> sched_getattr() is then called on the task, __getparam_dl() will > override kattr.sched_flags with the now out-of-date copy in dl_se->flags > and report the stale value to userspace. > > To fix this, make sure to only copy the flags that are relevant to > sched_deadline to and from the dl_se->flags field.
It also fixes the 'hidden' issue that a
uclampset -mX -MY -p dl_task
would end up at 'change:' label because of
dl_se->flags != attr->sched_flags
and not because of
attr->sched_flags & SCHED_FLAG_UTIL_CLAMP
And it also unblocks the uclamp-dl issue raised in https://lkml.kernel.org/r/ad30be79-8fb2-023d-9936-01f7173164e4@arm.com which surfaced when using `get_params()->__getparam_dl()` in SYSCALL_DEFINE3(sched_setattr,...). Just for reference, IIRC, you mentioned this already on irc.
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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