tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
1
fork

Configure Feed

Select the types of activity you want to include in your feed.

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 <juri.lelli@redhat.com>
Signed-off-by: Pingfan Liu <piliu@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://patch.msgid.link/20251125032630.8746-3-piliu@redhat.com

authored by

Pingfan Liu and committed by
Peter Zijlstra 64e6fa76 479972ef

+2 -1
+2 -1
kernel/sched/deadline.c
··· 3154 3154 struct rq *rq; 3155 3155 struct dl_bw *dl_b; 3156 3156 unsigned int cpu; 3157 - struct cpumask *msk = this_cpu_cpumask_var_ptr(local_cpu_mask_dl); 3157 + struct cpumask *msk; 3158 3158 3159 3159 raw_spin_lock_irqsave(&p->pi_lock, rf.flags); 3160 3160 if (!dl_task(p) || dl_entity_is_special(&p->dl)) { ··· 3162 3162 return; 3163 3163 } 3164 3164 3165 + msk = this_cpu_cpumask_var_ptr(local_cpu_mask_dl); 3165 3166 dl_get_task_effective_cpus(p, msk); 3166 3167 cpu = cpumask_first_and(cpu_active_mask, msk); 3167 3168 BUG_ON(cpu >= nr_cpu_ids);