Re: [PATCH v2 03/21] sched/deadline: Do not admit bandwidth for parameters that are kept

[Juri Lelli]

Hello,

On 04/11/26 16:11, Mathieu Desnoyers wrote:
> sys_sched_setattr() fills a SCHED_FLAG_KEEP_PARAMS request in from the
> task itself (get_params()), with no lock held, and
> __sched_setscheduler() then skips __setscheduler_params(): the task
> keeps the parameters it has, and its dl_bw with them.
> sched_dl_overflow() runs all the same.
> 
> A parameter change of the task's own that lands in between leaves the
> request stale, and dl_param_changed() takes it for a change: total_bw of
> the root domain, and this_bw and running_bw of its runqueue through
> dl_change_utilization(), then hold a bandwidth the task does not have,
> and the release at its 0-lag time, which takes the task's own dl_bw,
> leaves the difference behind.
> 
> There is nothing to admit for parameters that are kept: skip the check.
> 
> Found by reading, after the Sashiko AI review of the first posting of
> this series raised the case the previous patch refuses. Not reproduced:
> it needs a parameter change of a deadline task to land inside the window
> of a SCHED_FLAG_KEEP_PARAMS request on the same task.
> 
> Fixes: a509a7cd7974 ("sched/uclamp: Extend sched_setattr() to support utilization clamping")
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> ---

Reviewed-by: Juri Lelli <juri.lelli@xxxxxxxxxx>

Thanks,
Juri