{ "affected": [ { "ranges": [ { "events": [ { "introduced": "37c4efc1ddf98ba8b234d116d863a9464445901e" }, { "fixed": "5a541eb401acb89d791da41189d7a79220164b93" }, { "fixed": "37d6edb2f03b29399a3a337fae78674de51e1695" }, { "fixed": "3d122b2feb1dd76bb5041bdea5e1e1b007d8d415" }, { "fixed": "e7d7aa7b730178278109c41fa1b17b06873065d5" } ], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "type": "GIT" } ] }, { "package": { "ecosystem": "Linux", "name": "Kernel" }, "ranges": [ { "events": [ { "introduced": "5.1.0" }, { "fixed": "6.12.109" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.13.0" }, { "fixed": "6.18.50" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.19.0" }, { "fixed": "7.2.4" } ], "type": "ECOSYSTEM" } ] } ], "database_specific": { "cna_assigner": "Linux", "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89647.json" }, "details": "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-\u003etime` 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\u003e0`) 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 \u0026mdsc-\u003edentry_list_lock: 126180 128218 0.04 8063.44 15986965.20 124.69 1573354 5296812 0.04 8291.28 74164526.48 14.00\n -----------------------\n \u0026mdsc-\u003edentry_list_lock 111736 [\u003c000000007b11e319\u003e] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n \u0026mdsc-\u003edentry_list_lock 2631 [\u003c0000000050597999\u003e] __dentry_leases_walk+0x64/0x2c8\n \u0026mdsc-\u003edentry_list_lock 3878 [\u003c00000000c0022f62\u003e] __ceph_dentry_lease_touch+0x5c/0xa8\n \u0026mdsc-\u003edentry_list_lock 9973 [\u003c000000002f27cb6f\u003e] __dentry_lease_unlist+0x50/0xa0\n -----------------------\n \u0026mdsc-\u003edentry_list_lock 123621 [\u003c0000000050597999\u003e] __dentry_leases_walk+0x64/0x2c8\n \u0026mdsc-\u003edentry_list_lock 1822 [\u003c000000007b11e319\u003e] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n \u0026mdsc-\u003edentry_list_lock 2720 [\u003c000000002f27cb6f\u003e] __dentry_lease_unlist+0x50/0xa0\n \u0026mdsc-\u003edentry_list_lock 55 [\u003c00000000c0022f62\u003e] __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 \u0026mdsc-\u003edentry_list_lock: 1203 1215 0.16 408.88 33082.88 27.23 4320501 7357389 0.04 500.64 1961578.00 0.27\n -----------------------\n \u0026mdsc-\u003edentry_list_lock 1029 [\u003c000000003c9aea8a\u003e] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n \u0026mdsc-\u003edentry_list_lock 1\n---truncated---", "id": "CVE-2026-89647", "modified": "2026-09-13T03:30:31.732970642Z", "published": "2026-09-11T19:45:38.593Z", "references": [ { "type": "WEB", "url": "https://git.kernel.org/stable/c/37d6edb2f03b29399a3a337fae78674de51e1695" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/3d122b2feb1dd76bb5041bdea5e1e1b007d8d415" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/5a541eb401acb89d791da41189d7a79220164b93" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/e7d7aa7b730178278109c41fa1b17b06873065d5" }, { "type": "ADVISORY", "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89647.json" }, { "type": "ADVISORY", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89647" }, { "type": "PACKAGE", "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git" } ], "schema_version": "1.9.0", "summary": "ceph: do not repeat ceph_trim_dentries() if no progress possible" }