CVE-2026-98536 (GCVE-0-2026-98536)
Vulnerability from cvelistv5
Published
2026-10-18 15:18
Modified
2026-10-19 09:21
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: writeback: report a Tasks-RCU quiescent state per cgwb drain pass cleanup_offline_cgwbs_workfn() drains a dying cgwb by calling cleanup_offline_cgwb() until it returns false, with a cond_resched() between passes. On a CONFIG_PREEMPTION kernel that cond_resched() does nothing: _cond_resched() is a plain "return 0", and under PREEMPT_DYNAMIC the full and lazy modes disable it. Since commit 7dadeaa6e851 ("sched: Further restrict the preemption modes") those are the only two models on the architectures with PREEMPT_LAZY support, arm64 and x86 among them, so the drain loop never reports a Tasks-RCU quiescent state. A worker draining a cgwb with millions of attached inodes runs for minutes. On a 6.18 arm64 host in lazy mode the cgwb worker drained one dying cgroup's writeback domain for over 11 minutes. A BPF program unlink (bpf_trampoline_unlink_prog -> bpf_trampoline_update -> unregister_ftrace_direct -> ftrace_shutdown -> synchronize_rcu_tasks()) waited on that grace period while holding the trampoline mutex, 42 tasks queued behind it in D state, and the hung task detector fired at 614 s and panicked the host. Any BPF or ftrace detach during a long drain inherits the drain's length. Fix this by calling cond_resched_tasks_rcu_qs() so we do not stall out anybody who calls sycnrhonize_rcu_tasks(). We put this in a do { } while loop because if we have many small cgroups cleanup_offline_cgwb() will return false and we will never call cond_resched_tasks_rcu_qs(), creating the same problem.
References
Impacted products
Vendor Product Version
Linux Linux Version: c22d70a162d3cc177282c4487be4d54876ca55c8
Version: c22d70a162d3cc177282c4487be4d54876ca55c8
Version: c22d70a162d3cc177282c4487be4d54876ca55c8
Version: c22d70a162d3cc177282c4487be4d54876ca55c8
Version: c22d70a162d3cc177282c4487be4d54876ca55c8
Version: c22d70a162d3cc177282c4487be4d54876ca55c8
Version: c22d70a162d3cc177282c4487be4d54876ca55c8
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{
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      "descriptions": [
        {
          "lang": "en",
          "value": "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 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\u0027s writeback domain for over 11 minutes.  A BPF program unlink\n(bpf_trampoline_unlink_prog -\u003e bpf_trampoline_update -\u003e\nunregister_ftrace_direct -\u003e ftrace_shutdown -\u003e 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\u0027s 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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:21:19.730Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
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        {
          "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"
        }
      ],
      "title": "writeback: report a Tasks-RCU quiescent state per cgwb drain pass",
      "x_generator": {
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98536",
    "datePublished": "2026-10-18T15:18:04.013Z",
    "dateReserved": "2026-09-25T10:25:14.355Z",
    "dateUpdated": "2026-10-19T09:21:19.730Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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