{"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:\n\nceph: do not repeat ceph_trim_dentries() if no progress possible\n\nceph_cap_reclaim_work() re-queues itself for as long as\nceph_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","slug":"CVE-2026-89647","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nceph: do not repeat ceph_trim_dentries() if no progress possible\n\nceph_cap_reclaim_work() re-queues itself for as long as\nceph_trim_dentries() returns -EAGAIN, which happens whenever a lease\nwalk exhausts its `nr_to_scan` budget.  This creates a busy loop that\nconsumes CPU without making any progress when there is nothing to\nreclaim: with no cap pressure (`count==0`) and every scanned lease\nstill valid, each pass runs the full scan budget down to zero and\nreturns `-EAGAIN`, only to be queued again immediately.\n\nThe dir-lease walk made this worse.  When `expire_dir_lease` is\n`false` (i.e. we have no intention of reclaiming dir leases),\n__dir_lease_check() returned `TOUCH` for every valid lease.  `TOUCH`\nmoves the dentry to the tail of the list and resets `di->time` via\n__dentry_dir_lease_touch(), so a walk over N valid leases pointlessly\nrewrote the list, refreshed the timestamps (preventing them from ever\naging out) and always drained `nr_to_scan`, guaranteeing the `-EAGAIN`\nrequeue.\n\nFix this in three steps:\n\n - Return `KEEP` instead of `TOUCH` when `expire_dir_lease` is\n   `false`.  If we are not going to reclaim the lease, leave it in\n   place instead of churning the list and resetting its timestamp; the\n   walk then terminates naturally (or via `STOP` at the first fresh\n   lease).\n\n - Only return `-EAGAIN` from the first (dentry-lease) walk when something\n   was actually freed.  A full batch that frees nothing means retrying\n   the same list immediately is futile; fall through to the dir-lease\n   walk instead.\n\n - After both walks, bail out with success (0) when nothing was freed\n   and there is no cap pressure (`count==0`).  There is no reason to\n   keep retrying when we are not over the cap limit and made no\n   progress.\n\nUnder real cap pressure (`count>0`) the reclaim path is unchanged and\nstill retries via `-EAGAIN`.\n\nWithout this patch, I saw 500 ceph_trim_dentries() calls per second on\nour web servers.  This is very visible in `/proc/lock_stat` (5 minute\ncapture):\n\n              class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg\n\n &mdsc->dentry_list_lock:        126180         128218           0.04        8063.44    15986965.20         124.69        1573354        5296812           0.04        8291.28    74164526.48          14.00\n -----------------------\n &mdsc->dentry_list_lock         111736          [<000000007b11e319>] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n &mdsc->dentry_list_lock           2631          [<0000000050597999>] __dentry_leases_walk+0x64/0x2c8\n &mdsc->dentry_list_lock           3878          [<00000000c0022f62>] __ceph_dentry_lease_touch+0x5c/0xa8\n &mdsc->dentry_list_lock           9973          [<000000002f27cb6f>] __dentry_lease_unlist+0x50/0xa0\n -----------------------\n &mdsc->dentry_list_lock         123621          [<0000000050597999>] __dentry_leases_walk+0x64/0x2c8\n &mdsc->dentry_list_lock           1822          [<000000007b11e319>] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n &mdsc->dentry_list_lock           2720          [<000000002f27cb6f>] __dentry_lease_unlist+0x50/0xa0\n &mdsc->dentry_list_lock             55          [<00000000c0022f62>] __ceph_dentry_lease_touch+0x5c/0xa8\n\nWith this patch:\n\n              class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg\n\n &mdsc->dentry_list_lock:          1203           1215           0.16         408.88       33082.88          27.23        4320501        7357389           0.04         500.64     1961578.00           0.27\n -----------------------\n &mdsc->dentry_list_lock           1029          [<000000003c9aea8a>] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n &mdsc->dentry_list_lock            1\n---truncated---\n\n## Affected\n\n- `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < dd2e9824e5e7dba406005ff779a107f773175a76`\n- `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 5a541eb401acb89d791da41189d7a79220164b93`\n- `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 37d6edb2f03b29399a3a337fae78674de51e1695`\n- `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < 3d122b2feb1dd76bb5041bdea5e1e1b007d8d415`\n- `Linux >= 37c4efc1ddf98ba8b234d116d863a9464445901e < e7d7aa7b730178278109c41fa1b17b06873065d5`\n- `Linux 5.1`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **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)","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":223265,"id":"CVE-2026-89647","ts":1792180035519,"field":"cvss","old":"5.5","new":"7.5"},{"seq":223264,"id":"CVE-2026-89647","ts":1792180035519,"field":"severity","old":"medium","new":"high"},{"seq":208160,"id":"CVE-2026-89647","ts":1789922725678,"field":"cvss","old":"4.7","new":"5.5"},{"seq":202840,"id":"CVE-2026-89647","ts":1789403732620,"field":"cvss","old":"7.5","new":"4.7"},{"seq":202839,"id":"CVE-2026-89647","ts":1789403732620,"field":"severity","old":"high","new":"medium"},{"seq":197807,"id":"CVE-2026-89647","ts":1789384320484,"field":"cvss","old":"4.7","new":"7.5"},{"seq":197806,"id":"CVE-2026-89647","ts":1789384320484,"field":"severity","old":"medium","new":"high"},{"seq":183385,"id":"CVE-2026-89647","ts":1789356675144,"field":"cvss","old":"7.5","new":"4.7"},{"seq":183384,"id":"CVE-2026-89647","ts":1789356675144,"field":"severity","old":"high","new":"medium"},{"seq":153492,"id":"CVE-2026-89647","ts":1789285350781,"field":"cvss","old":null,"new":"7.5"},{"seq":153491,"id":"CVE-2026-89647","ts":1789285350781,"field":"severity","old":"none","new":"high"},{"seq":147494,"id":"CVE-2026-89647","ts":1789270211129,"field":"cvss","old":null,"new":"4.7"},{"seq":147493,"id":"CVE-2026-89647","ts":1789270211129,"field":"severity","old":"none","new":"medium"},{"seq":109246,"id":"CVE-2026-89647","ts":1789183731129,"field":"cvss","old":null,"new":"4.7"},{"seq":109245,"id":"CVE-2026-89647","ts":1789183731129,"field":"severity","old":"none","new":"medium"}]}