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Mon, 23 Mar 2026 04:12:08 -0700 (PDT) Received: from mi-HP-ProDesk-680-G6-PCI-Microtower-PC.mioffice.cn ([43.224.245.226]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c74665ca206sm8559228a12.18.2026.03.23.04.12.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2026 04:12:07 -0700 (PDT) From: zhidao su X-Google-Original-From: zhidao su To: sched-ext@lists.linux.dev Cc: linux-kernel@vger.kernel.org, tj@kernel.org, void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, peterz@infradead.org, mingo@redhat.com, zhidao su Subject: [PATCH] sched_ext: Use READ_ONCE() for bypass_depth in scx_bypass() Date: Mon, 23 Mar 2026 19:12:02 +0800 Message-ID: <20260323111202.3960280-1-suzhidao@xiaomi.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" In scx_bypass(), pos->bypass_depth is read under scx_sched_lock to update per-cpu BYPASSING flags: raw_spin_lock(&scx_sched_lock); scx_for_each_descendant_pre(pos, sch) { if (pos->bypass_depth) /* bare read */ However, bypass_depth is written by inc_bypass_depth() and dec_bypass_depth() under scx_bypass_lock (a different lock): lockdep_assert_held(&scx_bypass_lock); WRITE_ONCE(sch->bypass_depth, sch->bypass_depth + 1); The read side here holds scx_sched_lock, not scx_bypass_lock, so the two sides are protected by different locks, constituting a lockless concurrent access. All other read sites consistently use READ_ONCE(): L1237: if (unlikely(READ_ONCE(sch->bypass_depth))) L4083: while (likely(!READ_ONCE(sch->bypass_depth))) Add the missing READ_ONCE() for consistency with the rest of the code and to make the concurrency intent explicit to KCSAN. Signed-off-by: zhidao su --- kernel/sched/ext.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 72a07eb050a3..2654690e3661 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -5343,7 +5343,7 @@ static void scx_bypass(struct scx_sched *sch, bool by= pass) scx_for_each_descendant_pre(pos, sch) { struct scx_sched_pcpu *pcpu =3D per_cpu_ptr(pos->pcpu, cpu); =20 - if (pos->bypass_depth) + if (READ_ONCE(pos->bypass_depth)) pcpu->flags |=3D SCX_SCHED_PCPU_BYPASSING; else pcpu->flags &=3D ~SCX_SCHED_PCPU_BYPASSING; --=20 2.43.0