KEVWire

Security intelligence, with context.

Response snapshot Oct 30, 2026, 19:11 UTC

Back to the wire
Permalink
VulnerabilityCVE-2026-89647

Linux kernel: ceph: do not repeat ceph_trim_dentries() if no progress possible

In the Linux kernel, the following vulnerability has been resolved: ceph: do not repeat ceph_trim_dentries() if no progress possible ceph_cap_reclaim_work() re-queues itself for as long as ceph_trim_dentries() returns -EAGAIN, which happens whenever a lease walk exhausts its nr_to_scan budget.

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
0.6% in the next 30 days
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-89647 (opens a new tab)

What happened

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

ceph: do not repeat ceph_trim_dentries() if no progress possible

ceph_cap_reclaim_work() re-queues itself for as long as ceph_trim_dentries() returns -EAGAIN, which happens whenever a lease walk exhausts its nr_to_scan budget. This creates a busy loop that consumes CPU without making any progress when there is nothing to reclaim: with no cap pressure (count==0) and every scanned lease still valid, each pass runs the full scan budget down to zero and returns -EAGAIN, only to be queued again immediately.

The dir-lease walk made this worse. When expire_dir_lease is false (i.e. we have no intention of reclaiming dir leases), __dir_lease_check() returned TOUCH for every valid lease. TOUCH moves the dentry to the tail of the list and resets di->time via __dentry_dir_lease_touch(), so a walk over N valid leases pointlessly rewrote the list, refreshed the timestamps (preventing them from ever aging out) and always drained nr_to_scan, guaranteeing the -EAGAIN requeue.

Continue reading

Fix this in three steps:

- Return KEEP instead of TOUCH when expire_dir_lease is false. If we are not going to reclaim the lease, leave it in place instead of churning the list and resetting its timestamp; the walk then terminates naturally (or via STOP at the first fresh lease).

- Only return -EAGAIN from the first (dentry-lease) walk when something was actually freed. A full batch that frees nothing means retrying the same list immediately is futile; fall through to the dir-lease walk instead.

- After both walks, bail out with success (0) when nothing was freed and there is no cap pressure (count==0). There is no reason to keep retrying when we are not over the cap limit and made no progress.

Under real cap pressure (count>0) the reclaim path is unchanged and still retries via -EAGAIN.

Without this patch, I saw 500 ceph_trim_dentries() calls per second on our web servers. This is very visible in /proc/lock_stat (5 minute capture):

class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg

&mdsc->dentry_list_lock: 126180 128218 0.04 8063.44 15986965.20 124.69 1573354 5296812 0.04 8291.28 74164526.48 14.

00 ----------------------- &mdsc->dentry_list_lock 111736 [<000000007b11e319>] __ceph_dentry_dir_lease_touch+0x7c/0xa8 &mdsc->dentry_list_lock 2631 [<0000000050597999>] __dentry_leases_walk+0x64/0x2c8 &mdsc->dentry_list_lock 3878 [<00000000c0022f62>] __ceph_dentry_lease_touch+0x5c/0xa8 &mdsc->dentry_list_lock 9973 [<000000002f27cb6f>] __dentry_lease_unlist+0x50/0xa0 ----------------------- &mdsc->dentry_list_lock 123621 [<0000000050597999>] __dentry_leases_walk+0x64/0x2c8 &mdsc->dentry_list_lock 1822 [<000000007b11e319>] __ceph_dentry_dir_lease_touch+0x7c/0xa8 &mdsc->dentry_list_lock 2720 [<000000002f27cb6f>] __dentry_lease_unlist+0x50/0xa0 &mdsc->dentry_list_lock 55 [<00000000c0022f62>] __ceph_dentry_lease_touch+0x5c/0xa8

With this patch:

class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg

&mdsc->dentry_list_lock: 1203 1215 0.16 408.88 33082.88 27.23 4320501 7357389 0.04 500.64 1961578.00 0.27 ----------------------- &mdsc->dentry_list_lock 1029 [<000000003c9aea8a>] __ceph_dentry_dir_lease_touch+0x7c/0xa8 &mdsc->dentry_list_lock 1 ---truncated---

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.6%

Scored Percentile 49.8%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2026-89647 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  4. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  5. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-89647, scored 2026-10-30. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 30). Linux kernel: ceph: do not repeat ceph_trim_dentries() if no progress possible (CVE-2026-89647). https://kevwire.com/record/CVE-2026-89647

MLA

"Linux kernel: ceph: do not repeat ceph_trim_dentries() if no progress possible (CVE-2026-89647)." KEVWire, 30 Oct. 2026, kevwire.com/record/CVE-2026-89647.

Chicago

KEVWire. "Linux kernel: ceph: do not repeat ceph_trim_dentries() if no progress possible (CVE-2026-89647)." Last modified October 30, 2026. https://kevwire.com/record/CVE-2026-89647.

Evidence summary (plain text)

Linux kernel: ceph: do not repeat ceph_trim_dentries() if no progress possible (Sep 11, 2026).
In the Linux kernel, the following vulnerability has been resolved:

ceph: do not repeat ceph_trim_dentries() if no progress possible

ceph_cap_reclaim_work() re-queues itself for as long as
ceph_trim_dentries() returns -EAGAIN, which happens whenever a lease
walk exhausts its nr_to_scan budget.  This creates a busy loop that
consumes CPU without making any progress when there is nothing to
reclaim: with no cap pressure (count==0) and every scanned lease
still valid, each pass runs the full scan budget down to zero and
returns -EAGAIN, only to be queued again immediately.
CVSS 7.5 (version 3.1; evidence as of Oct 30, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-89647).
EPSS 0.6% for the following 30 days, scored Oct 30, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-89647&date=2026-10-30).
Sources:
NVD CVE-2026-89647: https://nvd.nist.gov/vuln/detail/CVE-2026-89647
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-30T13:06:45.042Z&lastModEndDate=2026-10-30T14:50:57.069Z&resultsPerPage=500&startIndex=500
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-30T12:22:16.957Z&lastModEndDate=2026-10-30T14:05:57.373Z&resultsPerPage=500&startIndex=500
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-30T11:45:59.009Z&lastModEndDate=2026-10-30T13:20:57.281Z&resultsPerPage=500&startIndex=500
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-89647&date=2026-10-30
Record ID: CVE-2026-89647.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 30, 2026, 14:52 UTC. Ingestion is not an independent editorial investigation.

NVD status: Received. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

Record JSON

Your account

Email alerts

Email alerts are coming as part of KEVWire Premium: join the waitlist. To follow your stack today, use its RSS feed, which honors your filters, or connect an AI agent through the API.

Suggest an improvement

Ideas, missing sources, corrections, and bugs are all welcome. No account needed. Suggestions are reviewed by a person before anything changes.

Record details

Record detail