From 03d958da4f355c380819a3baf339123c25db8e54 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 8 May 2026 13:48:29 -1000 Subject: [PATCH] sched_ext: Fix ops_cid layout assert ca1d48a86fab ("sched_ext: Use offsetofend on both sides of the ops_cid layout assert") replaced sizeof() with offsetofend() to dodge 32-bit PPC trailing padding, but the resulting check is tautological: with CID_OFFSET_MATCH(priv, priv) already enforcing offsetof(priv) equality and @priv being the same type in both structs, the two offsetofends are equal by construction. The original protection - catching a stray field added past @priv in sched_ext_ops_cid - is gone. Anchor on a zero-size __end[] marker appended after @priv. Its offset sits flush after @priv regardless of trailing struct padding; if a field is inserted past @priv, __end shifts and the assert fires. Closes: https://lore.kernel.org/all/20260508215211.0C03AC2BCB0@smtp.kernel.org/ Signed-off-by: Tejun Heo Reviewed-by: Emil Tsalapatis --- kernel/sched/ext.c | 6 ++---- kernel/sched/ext_internal.h | 3 +++ 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index f86ee15be7cb..b685f45b4fd0 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -10380,11 +10380,9 @@ static int __init scx_init(void) /* * cid-form must end exactly at @priv - validate_ops() skips * cpu_acquire/cpu_release for cid-form because reading those fields - * past the BPF allocation would be UB. offsetofend() on both sides - * instead of sizeof() on sched_ext_ops_cid to sidestep trailing - * struct padding (e.g. 32-bit PPC tail-pads ops_cid past @priv). + * past the BPF allocation would be UB. */ - BUILD_BUG_ON(offsetofend(struct sched_ext_ops_cid, priv) != + BUILD_BUG_ON(offsetof(struct sched_ext_ops_cid, __end) != offsetofend(struct sched_ext_ops, priv)); #undef CID_OFFSET_MATCH diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h index 0ed79bd891c7..cd33984cffcf 100644 --- a/kernel/sched/ext_internal.h +++ b/kernel/sched/ext_internal.h @@ -938,6 +938,9 @@ struct sched_ext_ops_cid { /* internal use only, must be NULL */ void __rcu *priv; + + /* layout end anchor for the BUILD_BUG_ON in scx_init(); keep last */ + char __end[0]; }; enum scx_opi {