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sched/deadline: Fix reset_on_fork reporting of DL tasks 

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
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override kattr.sched_flags with the now out-of-date copy in dl_se-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.

Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210727101103.2729607-2-qperret@google.com
This commit is contained in:
Quentin Perret 2021-07-27 11:11:01 +01:00 committed by Peter Zijlstra
parent f912d05161
commit f95091536f
2 changed files with 6 additions and 3 deletions
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7
kernel/sched/deadline.c
View File

@ -2741,7 +2741,7 @@ void __setparam_dl(struct task_struct *p, const struct sched_attr *attr)
dl_se->dl_runtime = attr->sched_runtime;
dl_se->dl_deadline = attr->sched_deadline;
dl_se->dl_period = attr->sched_period ?: dl_se->dl_deadline;
dl_se->flags = attr->sched_flags;
dl_se->flags = attr->sched_flags & SCHED_DL_FLAGS;
dl_se->dl_bw = to_ratio(dl_se->dl_period, dl_se->dl_runtime);
dl_se->dl_density = to_ratio(dl_se->dl_deadline, dl_se->dl_runtime);
}
@ -2754,7 +2754,8 @@ void __getparam_dl(struct task_struct *p, struct sched_attr *attr)
attr->sched_runtime = dl_se->dl_runtime;
attr->sched_deadline = dl_se->dl_deadline;
attr->sched_period = dl_se->dl_period;
attr->sched_flags = dl_se->flags;
attr->sched_flags &= ~SCHED_DL_FLAGS;
attr->sched_flags |= dl_se->flags;
}
/*
@ -2851,7 +2852,7 @@ bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr)
if (dl_se->dl_runtime != attr->sched_runtime ||
dl_se->dl_deadline != attr->sched_deadline ||
dl_se->dl_period != attr->sched_period ||
dl_se->flags != attr->sched_flags)
dl_se->flags != (attr->sched_flags & SCHED_DL_FLAGS))
return true;
return false;

2
kernel/sched/sched.h
View File

@ -227,6 +227,8 @@ static inline void update_avg(u64 *avg, u64 sample)
*/
#define SCHED_FLAG_SUGOV 0x10000000
#define SCHED_DL_FLAGS (SCHED_FLAG_RECLAIM | SCHED_FLAG_DL_OVERRUN | SCHED_FLAG_SUGOV)
static inline bool dl_entity_is_special(struct sched_dl_entity *dl_se)
{
#ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL