Description
In the Linux kernel, the following vulnerability has been resolved:

rcu/nocb: Fix missed RCU barrier on deoffloading

Currently, running rcutorture test with torture_type=rcu fwd_progress=8
n_barrier_cbs=8 nocbs_nthreads=8 nocbs_toggle=100 onoff_interval=60
test_boost=2, will trigger the following warning:

WARNING: CPU: 19 PID: 100 at kernel/rcu/tree_nocb.h:1061 rcu_nocb_rdp_deoffload+0x292/0x2a0
RIP: 0010:rcu_nocb_rdp_deoffload+0x292/0x2a0
Call Trace:
<TASK>
? __warn+0x7e/0x120
? rcu_nocb_rdp_deoffload+0x292/0x2a0
? report_bug+0x18e/0x1a0
? handle_bug+0x3d/0x70
? exc_invalid_op+0x18/0x70
? asm_exc_invalid_op+0x1a/0x20
? rcu_nocb_rdp_deoffload+0x292/0x2a0
rcu_nocb_cpu_deoffload+0x70/0xa0
rcu_nocb_toggle+0x136/0x1c0
? __pfx_rcu_nocb_toggle+0x10/0x10
kthread+0xd1/0x100
? __pfx_kthread+0x10/0x10
ret_from_fork+0x2f/0x50
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>

CPU0 CPU2 CPU3
//rcu_nocb_toggle //nocb_cb_wait //rcutorture

// deoffload CPU1 // process CPU1's rdp
rcu_barrier()
rcu_segcblist_entrain()
rcu_segcblist_add_len(1);
// len == 2
// enqueue barrier
// callback to CPU1's
// rdp->cblist
rcu_do_batch()
// invoke CPU1's rdp->cblist
// callback
rcu_barrier_callback()
rcu_barrier()
mutex_lock(&rcu_state.barrier_mutex);
// still see len == 2
// enqueue barrier callback
// to CPU1's rdp->cblist
rcu_segcblist_entrain()
rcu_segcblist_add_len(1);
// len == 3
// decrement len
rcu_segcblist_add_len(-2);
kthread_parkme()

// CPU1's rdp->cblist len == 1
// Warn because there is
// still a pending barrier
// trigger warning
WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
cpus_read_unlock();

// wait CPU1 to comes online and
// invoke barrier callback on
// CPU1 rdp's->cblist
wait_for_completion(&rcu_state.barrier_completion);
// deoffload CPU4
cpus_read_lock()
rcu_barrier()
mutex_lock(&rcu_state.barrier_mutex);
// block on barrier_mutex
// wait rcu_barrier() on
// CPU3 to unlock barrier_mutex
// but CPU3 unlock barrier_mutex
// need to wait CPU1 comes online
// when CPU1 going online will block on cpus_write_lock

The above scenario will not only trigger a WARN_ON_ONCE(), but also
trigger a deadlock.

Thanks to nocb locking, a second racing rcu_barrier() on an offline CPU
will either observe the decremented callback counter down to 0 and spare
the callback enqueue, or rcuo will observe the new callback and keep
rdp->nocb_cb_sleep to false.

Therefore check rdp->nocb_cb_sleep before parking to make sure no
further rcu_barrier() is waiting on the rdp.
Published: 2024-12-27
Score: 4.7 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
EUVD EUVD EUVD-2024-53195 In the Linux kernel, the following vulnerability has been resolved: rcu/nocb: Fix missed RCU barrier on deoffloading Currently, running rcutorture test with torture_type=rcu fwd_progress=8 n_barrier_cbs=8 nocbs_nthreads=8 nocbs_toggle=100 onoff_interval=60 test_boost=2, will trigger the following warning: WARNING: CPU: 19 PID: 100 at kernel/rcu/tree_nocb.h:1061 rcu_nocb_rdp_deoffload+0x292/0x2a0 RIP: 0010:rcu_nocb_rdp_deoffload+0x292/0x2a0 Call Trace: <TASK> ? __warn+0x7e/0x120 ? rcu_nocb_rdp_deoffload+0x292/0x2a0 ? report_bug+0x18e/0x1a0 ? handle_bug+0x3d/0x70 ? exc_invalid_op+0x18/0x70 ? asm_exc_invalid_op+0x1a/0x20 ? rcu_nocb_rdp_deoffload+0x292/0x2a0 rcu_nocb_cpu_deoffload+0x70/0xa0 rcu_nocb_toggle+0x136/0x1c0 ? __pfx_rcu_nocb_toggle+0x10/0x10 kthread+0xd1/0x100 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x2f/0x50 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> CPU0 CPU2 CPU3 //rcu_nocb_toggle //nocb_cb_wait //rcutorture // deoffload CPU1 // process CPU1's rdp rcu_barrier() rcu_segcblist_entrain() rcu_segcblist_add_len(1); // len == 2 // enqueue barrier // callback to CPU1's // rdp->cblist rcu_do_batch() // invoke CPU1's rdp->cblist // callback rcu_barrier_callback() rcu_barrier() mutex_lock(&rcu_state.barrier_mutex); // still see len == 2 // enqueue barrier callback // to CPU1's rdp->cblist rcu_segcblist_entrain() rcu_segcblist_add_len(1); // len == 3 // decrement len rcu_segcblist_add_len(-2); kthread_parkme() // CPU1's rdp->cblist len == 1 // Warn because there is // still a pending barrier // trigger warning WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist)); cpus_read_unlock(); // wait CPU1 to comes online and // invoke barrier callback on // CPU1 rdp's->cblist wait_for_completion(&rcu_state.barrier_completion); // deoffload CPU4 cpus_read_lock() rcu_barrier() mutex_lock(&rcu_state.barrier_mutex); // block on barrier_mutex // wait rcu_barrier() on // CPU3 to unlock barrier_mutex // but CPU3 unlock barrier_mutex // need to wait CPU1 comes online // when CPU1 going online will block on cpus_write_lock The above scenario will not only trigger a WARN_ON_ONCE(), but also trigger a deadlock. Thanks to nocb locking, a second racing rcu_barrier() on an offline CPU will either observe the decremented callback counter down to 0 and spare the callback enqueue, or rcuo will observe the new callback and keep rdp->nocb_cb_sleep to false. Therefore check rdp->nocb_cb_sleep before parking to make sure no further rcu_barrier() is waiting on the rdp.
History

Wed, 08 Oct 2025 14:00:00 +0000

Type Values Removed Values Added
Weaknesses NVD-CWE-noinfo
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Metrics cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

 cvssV3_1

{'score': 4.7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H'}

Mon, 30 Dec 2024 01:30:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate

Fri, 27 Dec 2024 14:15:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: rcu/nocb: Fix missed RCU barrier on deoffloading Currently, running rcutorture test with torture_type=rcu fwd_progress=8 n_barrier_cbs=8 nocbs_nthreads=8 nocbs_toggle=100 onoff_interval=60 test_boost=2, will trigger the following warning: WARNING: CPU: 19 PID: 100 at kernel/rcu/tree_nocb.h:1061 rcu_nocb_rdp_deoffload+0x292/0x2a0 RIP: 0010:rcu_nocb_rdp_deoffload+0x292/0x2a0 Call Trace: <TASK> ? __warn+0x7e/0x120 ? rcu_nocb_rdp_deoffload+0x292/0x2a0 ? report_bug+0x18e/0x1a0 ? handle_bug+0x3d/0x70 ? exc_invalid_op+0x18/0x70 ? asm_exc_invalid_op+0x1a/0x20 ? rcu_nocb_rdp_deoffload+0x292/0x2a0 rcu_nocb_cpu_deoffload+0x70/0xa0 rcu_nocb_toggle+0x136/0x1c0 ? __pfx_rcu_nocb_toggle+0x10/0x10 kthread+0xd1/0x100 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x2f/0x50 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> CPU0 CPU2 CPU3 //rcu_nocb_toggle //nocb_cb_wait //rcutorture // deoffload CPU1 // process CPU1's rdp rcu_barrier() rcu_segcblist_entrain() rcu_segcblist_add_len(1); // len == 2 // enqueue barrier // callback to CPU1's // rdp->cblist rcu_do_batch() // invoke CPU1's rdp->cblist // callback rcu_barrier_callback() rcu_barrier() mutex_lock(&rcu_state.barrier_mutex); // still see len == 2 // enqueue barrier callback // to CPU1's rdp->cblist rcu_segcblist_entrain() rcu_segcblist_add_len(1); // len == 3 // decrement len rcu_segcblist_add_len(-2); kthread_parkme() // CPU1's rdp->cblist len == 1 // Warn because there is // still a pending barrier // trigger warning WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist)); cpus_read_unlock(); // wait CPU1 to comes online and // invoke barrier callback on // CPU1 rdp's->cblist wait_for_completion(&rcu_state.barrier_completion); // deoffload CPU4 cpus_read_lock() rcu_barrier() mutex_lock(&rcu_state.barrier_mutex); // block on barrier_mutex // wait rcu_barrier() on // CPU3 to unlock barrier_mutex // but CPU3 unlock barrier_mutex // need to wait CPU1 comes online // when CPU1 going online will block on cpus_write_lock The above scenario will not only trigger a WARN_ON_ONCE(), but also trigger a deadlock. Thanks to nocb locking, a second racing rcu_barrier() on an offline CPU will either observe the decremented callback counter down to 0 and spare the callback enqueue, or rcuo will observe the new callback and keep rdp->nocb_cb_sleep to false. Therefore check rdp->nocb_cb_sleep before parking to make sure no further rcu_barrier() is waiting on the rdp.
Title rcu/nocb: Fix missed RCU barrier on deoffloading
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-05-11T20:54:27.563Z

Reserved: 2024-12-27T14:03:05.989Z

Link: CVE-2024-56547

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Analyzed

Published: 2024-12-27T14:15:34.497

Modified: 2025-10-08T13:57:18.497

Link: CVE-2024-56547

cve-icon Redhat

Severity : Moderate

Publid Date: 2024-12-27T00:00:00Z

Links: CVE-2024-56547 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2025-07-12T23:06:18Z

Weaknesses