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Merge: rcu: Fix rcu_read_unlock() deadloop due to softirq

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MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/2851

JIRA: https://issues.redhat.com/browse/RHEL-178446

There is a deadloop in rcu_read_unlock() that can be hit by ftrace (in particular while running the LTP ftrace-stress-test). When this happened, other processes get stuck in softlockup.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Approved-by: Phil Auld <pauld@redhat.com>
Approved-by: Waiman Long <longman@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>
This commit is contained in:
CKI KWF Bot
2026-09-01 07:27:19 +00:00
parent afa81ddbe0 756d361463
commit 85753d3e48
2 changed files with 10 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/rcu/tree.h
+1 -1
View File
@@ -203,7 +203,7 @@ struct rcu_data {
/* during and after the last grace */
/* period it is aware of. */
struct irq_work defer_qs_iw; /* Obtain later scheduler attention. */
int defer_qs_iw_pending; /* Scheduler attention pending? */
int defer_qs_pending; /* irqwork or softirq pending? */
struct work_struct strict_work; /* Schedule readers for strict GPs. */
/* 2) batch handling */
kernel/rcu/tree_plugin.h
+8 -5
View File
@@ -487,8 +487,8 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
union rcu_special special;
rdp = this_cpu_ptr(&rcu_data);
if (rdp->defer_qs_iw_pending == DEFER_QS_PENDING)
rdp->defer_qs_iw_pending = DEFER_QS_IDLE;
if (rdp->defer_qs_pending == DEFER_QS_PENDING)
rdp->defer_qs_pending = DEFER_QS_IDLE;
/*
* If RCU core is waiting for this CPU to exit its critical section,
@@ -646,7 +646,7 @@ static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
* 5. Deferred QS reporting does not happen.
*/
if (rcu_preempt_depth() > 0)
WRITE_ONCE(rdp->defer_qs_iw_pending, DEFER_QS_IDLE);
WRITE_ONCE(rdp->defer_qs_pending, DEFER_QS_IDLE);
local_irq_restore(flags);
}
@@ -750,7 +750,10 @@ static void rcu_read_unlock_special(struct task_struct *t)
// Using softirq, safe to awaken, and either the
// wakeup is free or there is either an expedited
// GP in flight or a potential need to deboost.
if (rdp->defer_qs_pending != DEFER_QS_PENDING) {
rdp->defer_qs_pending = DEFER_QS_PENDING;
raise_softirq_irqoff(RCU_SOFTIRQ);
}
} else {
// Enabling BH or preempt does reschedule, so...
// Also if no expediting and no possible deboosting,
@@ -759,11 +762,11 @@ static void rcu_read_unlock_special(struct task_struct *t)
set_tsk_need_resched(current);
set_preempt_need_resched();
if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
needs_exp && rdp->defer_qs_iw_pending != DEFER_QS_PENDING &&
needs_exp && rdp->defer_qs_pending != DEFER_QS_PENDING &&
cpu_online(rdp->cpu)) {
// Get scheduler to re-evaluate and call hooks.
// If !IRQ_WORK, FQS scan will eventually IPI.
rdp->defer_qs_iw_pending = DEFER_QS_PENDING;
rdp->defer_qs_pending = DEFER_QS_PENDING;
irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
}
}