FKIE_CVE-2026-98536

Vulnerability from fkie_nvd - Published: 2026-10-18 16:17 - Updated: 2026-10-19 10:19
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
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/260f586a80e7f624dd7f069898a75a904f34d373
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/407a5d205179a4ab186571b0e16ec42725dc77bc
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/42462b5bb0dec57db7f85d0f77655c737d45754d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4eb889649eaf65f4a5727b04ba1c017b7d05bb16
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/863049b4018237d1590cd13b16e9fe9c0faad2c6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ebf1555ad2821be06f87a88ffd9a2cab8d2200e1
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/fd3bf32279df98751364b3609eb100a3e42f253b
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/backing-dev.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "863049b4018237d1590cd13b16e9fe9c0faad2c6",
              "status": "affected",
              "version": "c22d70a162d3cc177282c4487be4d54876ca55c8",
              "versionType": "git"
            },
            {
              "lessThan": "42462b5bb0dec57db7f85d0f77655c737d45754d",
              "status": "affected",
              "version": "c22d70a162d3cc177282c4487be4d54876ca55c8",
              "versionType": "git"
            },
            {
              "lessThan": "ebf1555ad2821be06f87a88ffd9a2cab8d2200e1",
              "status": "affected",
              "version": "c22d70a162d3cc177282c4487be4d54876ca55c8",
              "versionType": "git"
            },
            {
              "lessThan": "4eb889649eaf65f4a5727b04ba1c017b7d05bb16",
              "status": "affected",
              "version": "c22d70a162d3cc177282c4487be4d54876ca55c8",
              "versionType": "git"
            },
            {
              "lessThan": "fd3bf32279df98751364b3609eb100a3e42f253b",
              "status": "affected",
              "version": "c22d70a162d3cc177282c4487be4d54876ca55c8",
              "versionType": "git"
            },
            {
              "lessThan": "260f586a80e7f624dd7f069898a75a904f34d373",
              "status": "affected",
              "version": "c22d70a162d3cc177282c4487be4d54876ca55c8",
              "versionType": "git"
            },
            {
              "lessThan": "407a5d205179a4ab186571b0e16ec42725dc77bc",
              "status": "affected",
              "version": "c22d70a162d3cc177282c4487be4d54876ca55c8",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "mm/backing-dev.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.14"
            },
            {
              "lessThan": "5.14",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.222",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.189",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.158",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.112",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.55",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "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."
    }
  ],
  "id": "CVE-2026-98536",
  "lastModified": "2026-10-19T10:19:09.220",
  "metrics": {},
  "published": "2026-10-18T16:17:05.357",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/260f586a80e7f624dd7f069898a75a904f34d373"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/407a5d205179a4ab186571b0e16ec42725dc77bc"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/42462b5bb0dec57db7f85d0f77655c737d45754d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/4eb889649eaf65f4a5727b04ba1c017b7d05bb16"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/863049b4018237d1590cd13b16e9fe9c0faad2c6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ebf1555ad2821be06f87a88ffd9a2cab8d2200e1"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fd3bf32279df98751364b3609eb100a3e42f253b"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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