{"id":"CVE-2026-98818","summary":"mm/slab: do not wake up kswapd in __kfree_rcu_sheaf()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/slab: do not wake up kswapd in __kfree_rcu_sheaf()\n\nSince kfree_rcu() can be called under pi_lock (a raw spinlock in the\nscheduler), kfree_rcu() itself should never allocate memory with\n__GFP_KSWAPD_RECLAIM as waking up kswapd ends up acquiring pi_lock,\nwhich leads to a deadlock.\n\nReproducing the issue even intentionally was not straightforward.\nThe set_cpus_allowed_force() path that is called under pi_lock is\nexercised very rarely, and competing tasks that allocate memory will\nmost likely wake kswapd up.\n\nTherefore the existence of the deadlock was verified with a modified\nkernel that has a lockdep map for waking up kswapd:\n\n  ======================================================\n  WARNING: possible circular locking dependency detected\n  7.2.0-rc1-slab-for-next+ #10 Not tainted\n  ------------------------------------------------------\n  git/6660 is trying to acquire lock:\n  ffff8e524533c550 (&p-\u003epi_lock){-.-.}-{2:2}, at: _raw_spin_lock_irqsave+0x12/0x20\n\n  but task is already holding lock:\n  ffff8e57bffff1a0 (&pgdat-\u003ekswapd_wait){....}-{3:3}, at: _raw_spin_lock_irqsave+0x12/0x20\n\n  which lock already depends on the new lock.\n\n  the existing dependency chain (in reverse order) is:\n\n  -\u003e #2 (&pgdat-\u003ekswapd_wait){....}-{3:3}:\n         __lock_acquire+0x5a4/0xc50\n         lock_acquire.part.0+0xb7/0x240\n         lock_acquire+0x70/0x170\n         __raw_spin_lock_irqsave+0x44/0x80\n         _raw_spin_lock_irqsave+0x12/0x20\n         __wake_up_common_lock+0x31/0xa0\n         __wake_up+0x20/0x40\n         kswapd_wakeup_wake+0x7e/0x110\n         wakeup_kswapd+0x295/0x320\n         wake_all_kswapds+0xac/0x1a0\n         __alloc_pages_slowpath.constprop.0+0x282/0xf80\n         __alloc_frozen_pages_noprof+0x32a/0x360\n         alloc_slab_page+0x2e/0x160\n         allocate_slab+0x82/0x420\n         new_slab+0x52/0xb0\n         refill_objects+0x13d/0x190\n         refill_sheaf+0x5d/0xd0\n         __pcs_replace_empty_main+0x230/0xb10\n         [...]\n\n  -\u003e #1 (kswapd_wakeup){-.-.}-{0:0}:\n         __lock_acquire+0x5a4/0xc50\n         lock_sync.part.0+0x75/0x100\n         lock_sync+0x36/0x70\n         might_wakeup_kswapd+0x61/0xa0\n         __kfree_rcu_sheaf+0x33/0xd90\n         kvfree_call_rcu+0x1d4/0x3b0\n         set_cpus_allowed_force+0x163/0x220\n         cpuset_cpus_allowed_fallback+0x18b/0x240\n         select_fallback_rq+0x1e6/0x250\n\t [...]\n\n  -\u003e #0 (&p-\u003epi_lock){-.-.}-{2:2}:\n         check_prev_add+0xe6/0xe00\n         validate_chain+0x51e/0x6e0\n         __lock_acquire+0x5a4/0xc50\n         lock_acquire.part.0+0xb7/0x240\n         lock_acquire+0x70/0x170\n         __raw_spin_lock_irqsave+0x44/0x80\n         _raw_spin_lock_irqsave+0x12/0x20\n         try_to_wake_up+0x77/0xa90\n         default_wake_function+0x27/0x60\n         autoremove_wake_function+0x23/0xb0\n         __wake_up_common+0xb8/0x170\n         __wake_up_common_lock+0x51/0xa0\n         __wake_up+0x20/0x40\n         kswapd_wakeup_wake+0x7e/0x110\n         wakeup_kswapd+0x295/0x320\n         wake_all_kswapds+0xac/0x1a0\n         __alloc_pages_slowpath.constprop.0+0x282/0xf80\n         __alloc_frozen_pages_noprof+0x32a/0x360\n         alloc_slab_page+0x2e/0x160\n         allocate_slab+0x82/0x420\n         new_slab+0x52/0xb0\n         refill_objects+0x13d/0x190\n         refill_sheaf+0x5d/0xd0\n         __pcs_replace_empty_main+0x230/0xb10\n         [...]\n\n  other info that might help us debug this:\n\n  Chain exists of:\n    &p-\u003epi_lock --\u003e kswapd_wakeup --\u003e &pgdat-\u003ekswapd_wait\n\n   Possible unsafe locking scenario:\n\n         CPU0                    CPU1\n         ----                    ----\n    lock(&pgdat-\u003ekswapd_wait);\n                                 lock(kswapd_wakeup);\n                                 lock(&pgdat-\u003ekswapd_wait);\n    lock(&p-\u003epi_lock);\n\n   *** DEADLOCK ***\n\n  3 locks held by git/6660:\n   #0: ffff8e519f0e9e20 (&type-\u003ei_mutex_dir_key#6){++++}-{4:4}, at: lookup_slow+0x2d/0x60\n   #1: ffffffff8a31c460 (kswapd_wakeup){-.-.}-\n---truncated---","modified":"2026-10-20T02:30:47.593065641Z","published":"2026-10-18T15:49:10.258Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98818.json"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/46545c86b54ffb969b6e3662942b4a6191619eaa"},{"type":"WEB","url":"https://git.kernel.org/stable/c/af2fb3ee6679b517e2fdbd3ba16ec276a8b74312"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98818.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98818"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"ec66e0d599520ab414db745544e25d80d0ac5054"},{"fixed":"46545c86b54ffb969b6e3662942b4a6191619eaa"},{"fixed":"af2fb3ee6679b517e2fdbd3ba16ec276a8b74312"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98818.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.18.0"},{"fixed":"7.2.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98818.json"}}],"schema_version":"1.9.0"}