{"cve":"CVE-2026-89647","nvd":{"published":"2026-09-11T20:19:50.607","modified":"2026-10-21T13:20:14.977","status":"Received","description":"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 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---","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":[],"references":["https://git.kernel.org/stable/c/37d6edb2f03b29399a3a337fae78674de51e1695","https://git.kernel.org/stable/c/3d122b2feb1dd76bb5041bdea5e1e1b007d8d415","https://git.kernel.org/stable/c/5a541eb401acb89d791da41189d7a79220164b93","https://git.kernel.org/stable/c/dd2e9824e5e7dba406005ff779a107f773175a76","https://git.kernel.org/stable/c/e7d7aa7b730178278109c41fa1b17b06873065d5"],"products":[],"source":"nvd","synced_at":"2026-10-22T16:41:11.231219466+00:00"},"epss":{"cve":"CVE-2026-89647","score":0.00622,"percentile":0.49498,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}