--- id: CVE-2026-89647 title: 'ceph: do not repeat ceph_trim_dentries() if no progress possible' summary: |- 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 ha… severity: high cvss: 7.5 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H' cvssSource: cna cwe: - CWE-835 vendor: Linux product: Linux affected: - >- Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < dd2e9824e5e7dba406005ff779a107f773175a76 - >- Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 5a541eb401acb89d791da41189d7a79220164b93 - >- Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 37d6edb2f03b29399a3a337fae78674de51e1695 - >- Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 3d122b2feb1dd76bb5041bdea5e1e1b007d8d415 - >- Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < e7d7aa7b730178278109c41fa1b17b06873065d5 - Linux 5.1 ssvc: exploitation: none automatable: 'yes' technicalImpact: partial timestamp: '2026-10-16T19:25:05.998836Z' published: '2026-09-11' updated: '2026-10-21' sourceUpdated: '2026-10-21T12:48:11.164Z' source: CVEORG sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89647' references: - url: 'https://git.kernel.org/stable/c/dd2e9824e5e7dba406005ff779a107f773175a76' - url: 'https://git.kernel.org/stable/c/5a541eb401acb89d791da41189d7a79220164b93' - url: 'https://git.kernel.org/stable/c/37d6edb2f03b29399a3a337fae78674de51e1695' - url: 'https://git.kernel.org/stable/c/3d122b2feb1dd76bb5041bdea5e1e1b007d8d415' - url: 'https://git.kernel.org/stable/c/e7d7aa7b730178278109c41fa1b17b06873065d5' - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89647.json - url: 'https://access.redhat.com/security/cve/CVE-2026-89647' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532249' - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89647' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89647' - url: >- https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89647.mbox tags: - cve.org - csaf - vex - red-hat - score-dispute epss: 0.00622 epssPercentile: 0.4959 scores: cna: 7.5 vendor: 5.5 ingestedAt: '2026-09-14T15:23:07.473Z' --- ## Overview 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. 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--- ## Affected - `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < dd2e9824e5e7dba406005ff779a107f773175a76` - `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 5a541eb401acb89d791da41189d7a79220164b93` - `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 37d6edb2f03b29399a3a337fae78674de51e1695` - `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 3d122b2feb1dd76bb5041bdea5e1e1b007d8d415` - `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < e7d7aa7b730178278109c41fa1b17b06873065d5` - `Linux 5.1` ## Remediation Refer to the linked advisories for vendor-supplied fixes and affected version ranges. ## Vendor advisories - **Red Hat VEX** · Low · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89647.json)