rcu/nocb: Fix WARN_ON_ONCE() in the rcu_nocb_bypass_lock()

Summary

In the Linux kernel, the following vulnerability has been resolved: rcu/nocb: Fix WARN_ON_ONCE() in the rcu_nocb_bypass_lock() For the kernels built with CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y and CONFIG_RCU_LAZY=y, the following scenarios will trigger WARN_ON_ONCE() in the rcu_nocb_bypass_lock() and rcu_nocb_wait_contended() functions: CPU2 CPU11 kthread rcu_nocb_cb_kthread ksys_write rcu_do_batch vfs_write rcu_torture_timer_cb proc_sys_write __kmem_cache_free proc_sys_call_handler kmemleak_free drop_caches_sysctl_handler delete_object_full drop_slab __delete_object shrink_slab put_object lazy_rcu_shrink_scan call_rcu rcu_nocb_flush_bypass __call_rcu_commn rcu_nocb_bypass_lock raw_spin_trylock(&rdp->nocb_bypass_lock) fail atomic_inc(&rdp->nocb_lock_contended); rcu_nocb_wait_contended WARN_ON_ONCE(smp_processor_id() != rdp->cpu); WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)) | |_ _ _ _ _ _ _ _ _ same rdp and rdp->cpu != 11 _ _ _ _ _ _ _ _ __| Reproduce this bug with "echo 3 > /proc/sys/vm/drop_caches". This commit therefore uses rcu_nocb_try_flush_bypass() instead of rcu_nocb_flush_bypass() in lazy_rcu_shrink_scan(). If the nocb_bypass queue is being flushed, then rcu_nocb_try_flush_bypass will return directly.

Timeline

1. May 19, 2024, 10:10 AM UTCCVE published
2. May 23, 2024, 7:21 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. May 11, 2026, 8:13 PM UTCRecord last updated

Affected versions

• Linux Linux

  Version range not reported

• Linux Linux

  6.5

References 3