From: Pingfan Liu Date: Tue, 25 Nov 2025 03:26:30 +0000 (+0800) Subject: sched/deadline: Fix potential race in dl_add_task_root_domain() X-Git-Tag: v6.19-rc6~12^2~8 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=64e6fa76610ec970cfa8296ed057907a4b384ca5;p=thirdparty%2Flinux.git sched/deadline: Fix potential race in dl_add_task_root_domain() The access rule for local_cpu_mask_dl requires it to be called on the local CPU with preemption disabled. However, dl_add_task_root_domain() currently violates this rule. Without preemption disabled, the following race can occur: 1. ThreadA calls dl_add_task_root_domain() on CPU 0 2. Gets pointer to CPU 0's local_cpu_mask_dl 3. ThreadA is preempted and migrated to CPU 1 4. ThreadA continues using CPU 0's local_cpu_mask_dl 5. Meanwhile, the scheduler on CPU 0 calls find_later_rq() which also uses local_cpu_mask_dl (with preemption properly disabled) 6. Both contexts now corrupt the same per-CPU buffer concurrently Fix this by moving the local_cpu_mask_dl access to the preemption disabled section. Closes: https://lore.kernel.org/lkml/aSBjm3mN_uIy64nz@jlelli-thinkpadt14gen4.remote.csb Fixes: 318e18ed22e8 ("sched/deadline: Walk up cpuset hierarchy to decide root domain when hot-unplug") Reported-by: Juri Lelli Signed-off-by: Pingfan Liu Signed-off-by: Peter Zijlstra (Intel) Acked-by: Juri Lelli Acked-by: Waiman Long Link: https://patch.msgid.link/20251125032630.8746-3-piliu@redhat.com --- diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 463ba50f9fff..e3efc40349f1 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -3154,7 +3154,7 @@ void dl_add_task_root_domain(struct task_struct *p) struct rq *rq; struct dl_bw *dl_b; unsigned int cpu; - struct cpumask *msk = this_cpu_cpumask_var_ptr(local_cpu_mask_dl); + struct cpumask *msk; raw_spin_lock_irqsave(&p->pi_lock, rf.flags); if (!dl_task(p) || dl_entity_is_special(&p->dl)) { @@ -3162,6 +3162,7 @@ void dl_add_task_root_domain(struct task_struct *p) return; } + msk = this_cpu_cpumask_var_ptr(local_cpu_mask_dl); dl_get_task_effective_cpus(p, msk); cpu = cpumask_first_and(cpu_active_mask, msk); BUG_ON(cpu >= nr_cpu_ids);