{"id":"CVE-2026-98536","title":"writeback: report a Tasks-RCU quiescent state per cgwb drain pass","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nwriteback: report a Tasks-RCU quiescent state per cgwb drain pass\n\ncleanup_offline_cgwbs_workfn() drains a dying cgwb by calling\ncleanup_offline_cgwb() until it returns…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 863049b4018237d1590cd13b16e9fe9c0faad2c6","Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 42462b5bb0dec57db7f85d0f77655c737d45754d","Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < ebf1555ad2821be06f87a88ffd9a2cab8d2200e1","Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 4eb889649eaf65f4a5727b04ba1c017b7d05bb16","Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < fd3bf32279df98751364b3609eb100a3e42f253b","Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 260f586a80e7f624dd7f069898a75a904f34d373","Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 407a5d205179a4ab186571b0e16ec42725dc77bc","Linux 5.14"],"published":"2026-10-18","updated":"2026-10-18","sourceUpdated":"2026-10-18T15:18:04.013Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98536","references":[{"url":"https://git.kernel.org/stable/c/863049b4018237d1590cd13b16e9fe9c0faad2c6"},{"url":"https://git.kernel.org/stable/c/42462b5bb0dec57db7f85d0f77655c737d45754d"},{"url":"https://git.kernel.org/stable/c/ebf1555ad2821be06f87a88ffd9a2cab8d2200e1"},{"url":"https://git.kernel.org/stable/c/4eb889649eaf65f4a5727b04ba1c017b7d05bb16"},{"url":"https://git.kernel.org/stable/c/fd3bf32279df98751364b3609eb100a3e42f253b"},{"url":"https://git.kernel.org/stable/c/260f586a80e7f624dd7f069898a75a904f34d373"},{"url":"https://git.kernel.org/stable/c/407a5d205179a4ab186571b0e16ec42725dc77bc"}],"tags":["cve.org"],"ingestedAt":"2026-10-18T15:45:12.277Z","slug":"CVE-2026-98536","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nwriteback: report a Tasks-RCU quiescent state per cgwb drain pass\n\ncleanup_offline_cgwbs_workfn() drains a dying cgwb by calling\ncleanup_offline_cgwb() until it returns false, with a cond_resched()\nbetween passes.  On a CONFIG_PREEMPTION kernel that cond_resched() does\nnothing: _cond_resched() is a plain \"return 0\", and under PREEMPT_DYNAMIC\nthe full and lazy modes disable it.  Since commit 7dadeaa6e851 (\"sched:\nFurther restrict the preemption modes\") those are the only two models on\nthe architectures with PREEMPT_LAZY support, arm64 and x86 among them, so\nthe drain loop never reports a Tasks-RCU quiescent state.\n\nA worker draining a cgwb with millions of attached inodes runs for\nminutes.  On a 6.18 arm64 host in lazy mode the cgwb worker drained one\ndying cgroup's writeback domain for over 11 minutes.  A BPF program unlink\n(bpf_trampoline_unlink_prog -> bpf_trampoline_update ->\nunregister_ftrace_direct -> ftrace_shutdown -> synchronize_rcu_tasks())\nwaited on that grace period while holding the trampoline mutex, 42 tasks\nqueued behind it in D state, and the hung task detector fired at 614 s and\npanicked the host.  Any BPF or ftrace detach during a long drain inherits\nthe drain's length.\n\nFix this by calling cond_resched_tasks_rcu_qs() so we do not stall out\nanybody who calls sycnrhonize_rcu_tasks().  We put this in a do { } while\nloop because if we have many small cgroups cleanup_offline_cgwb() will\nreturn false and we will never call cond_resched_tasks_rcu_qs(), creating\nthe same problem.\n\n## Affected\n\n- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 863049b4018237d1590cd13b16e9fe9c0faad2c6`\n- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 42462b5bb0dec57db7f85d0f77655c737d45754d`\n- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < ebf1555ad2821be06f87a88ffd9a2cab8d2200e1`\n- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 4eb889649eaf65f4a5727b04ba1c017b7d05bb16`\n- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < fd3bf32279df98751364b3609eb100a3e42f253b`\n- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 260f586a80e7f624dd7f069898a75a904f34d373`\n- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 407a5d205179a4ab186571b0e16ec42725dc77bc`\n- `Linux 5.14`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}