In the Linux kernel, the following vulnerability has been resolved:
mm/vmscan: report RCU-tasks quiescent states in shrink_lruvec()
I am seeing some rcu_tasks stalls in the Meta fleet during reclaim.
INFO: rcu_tasks detected stalls on tasks:
0000000088620d09: .. nvcsw: 6735/6735 holdout: 1 idle_cpu: -1/8
task:GlobalCPUThread state:R running task pid:2552016 tgid:2524552
Call Trace:
shrink_lruvec
mem_cgroup_iter
shrink_node
do_try_to_free_pages
try_to_free_pages
__alloc_frozen_pages_noprof
alloc_pages_noprof
pte_alloc_one
__pte_alloc
handle_mm_fault
Nothing promises direct reclaim returns in bounded time, and the scan loop
in shrink_lruvec() only calls cond_resched(), which is a no-op on
PREEMPTION kernels. Involuntary preemption is not a Tasks-RCU quiescent
state, so the reclaiming task never reports one and becomes a holdout.
Upgrade it to cond_resched_tasks_rcu_qs(), which reports a quiescent state
even when cond_resched() does nothing.
PS: This has been discussed in [1]
