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    Subject[PATCH 4.19 035/293] sched/deadline: Fix reset_on_fork reporting of DL tasks
    Date
    From: Quentin Perret <qperret@google.com>

    [ Upstream commit f95091536f78971b269ec321b057b8d630b0ad8a ]

    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    override kattr.sched_flags with the now out-of-date copy in dl_se-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
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/sched/deadline.c | 7 ++++---
    kernel/sched/sched.h | 2 ++
    2 files changed, 6 insertions(+), 3 deletions(-)

    diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
    index aa592dc3cb40..9b2bb5f3ce09 100644
    --- a/kernel/sched/deadline.c
    +++ b/kernel/sched/deadline.c
    @@ -2615,7 +2615,7 @@ 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);
    }
    @@ -2628,7 +2628,8 @@ 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;
    }

    /*
    @@ -2703,7 +2704,7 @@ 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;
    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index 7b7ba91e319b..55e695080fc6 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -209,6 +209,8 @@ static inline int task_has_dl_policy(struct task_struct *p)
    */
    #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
    --
    2.30.2


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