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sched_ext: Explain the temporary situation around scx_root dereferences

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Naked scx_root dereferences are being used as temporary markers to indicate
that they need to be updated to point to the right scheduler instance.
Explain the situation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2025-05-14 12:37:18 -04:00
parent a8433f7a26
commit cb4ff91492
1 changed files with 8 additions and 0 deletions
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8
kernel/sched/ext.c
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@ -1016,6 +1016,14 @@ enum scx_ops_state {
#define SCX_OPSS_STATE_MASK ((1LU << SCX_OPSS_QSEQ_SHIFT) - 1)
#define SCX_OPSS_QSEQ_MASK (~SCX_OPSS_STATE_MASK)
/*
* NOTE: sched_ext is in the process of growing multiple scheduler support and
* scx_root usage is in a transitional state. Naked dereferences are safe if the
* caller is one of the tasks attached to SCX and explicit RCU dereference is
* necessary otherwise. Naked scx_root dereferences trigger sparse warnings but
* are used as temporary markers to indicate that the dereferences need to be
* updated to point to the associated scheduler instances rather than scx_root.
*/
static struct scx_sched __rcu *scx_root;
/*