diff options
| author | Hui Su <sh_def@163.com> | 2026-10-21 18:12:14 +0900 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2026-10-21 11:30:03 -1000 |
| commit | 651694bc47a15b99e756ebb27f4e6be6d59bf397 (patch) | |
| tree | 26bab9f498c2adc7965cd1e8c17b8887787b479d | |
| parent | 3b1c7c74a6da97f86bdd31c66e8c592aa4372e16 (diff) | |
sched_ext: Reject oversized automatic CID shards
Automatic topology packing starts a new shard before adding a core when
the current shard would exceed its target size. However, a first core is
always accepted so that cores remain indivisible. An indivisible core with
more than SCX_CID_SHARD_MAX_CPUS CPUs cannot be represented without
exceeding the hard shard limit.
Per-shard state uses fixed-size inline cmask storage sized for
SCX_CID_SHARD_MAX_CPUS. Passing an oversized shard to alloc_pshard() can
therefore make cmask initialization overwrite the following fields.
Reject an indivisible core larger than SCX_CID_SHARD_MAX_CPUS before adding
it to a shard. Existing non-empty shard splitting already keeps the total
within the hard cap, while an indivisible core may still exceed
cid_shard_size when it fits within the hard limit.
Report the oversized core and the hard limit with scx_error() so that the
rejection is diagnosable.
tj: The bug is only reproducible with artificial VM topologies. It can't
happen on real hardware.
Fixes: e2c841b91bf9 ("sched_ext: Add CID sharding")
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Tested-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Hui Su <sh_def@163.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
| -rw-r--r-- | kernel/sched/ext/cid.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/sched/ext/cid.c b/kernel/sched/ext/cid.c index 9fc219257004..20e40e3fe8ff 100644 --- a/kernel/sched/ext/cid.c +++ b/kernel/sched/ext/cid.c @@ -309,6 +309,12 @@ s32 scx_cid_init(struct scx_sched *sch) * empty shard. */ cids_in_core = cpumask_weight(core_scratch); + if (cids_in_core > SCX_CID_SHARD_MAX_CPUS) { + scx_error(sch, "core with %u cpus exceeds max shard size %d", + cids_in_core, SCX_CID_SHARD_MAX_CPUS); + return -E2BIG; + } + max_cores = cores_per_shard + (shard_local < nr_large ? 1 : 0); if (cores_in_shard && (cores_in_shard >= max_cores || |