{"id":"CVE-2026-98536","published":"2026-10-18T16:17:05.357","lastModified":"2026-10-19T10:19:09.220","description":"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'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.","cvssScore":null,"cvssSeverity":null,"cvssVector":null,"cwes":[],"vendors":[],"products":[],"references":[{"url":"https://git.kernel.org/stable/c/260f586a80e7f624dd7f069898a75a904f34d373","tags":[]},{"url":"https://git.kernel.org/stable/c/407a5d205179a4ab186571b0e16ec42725dc77bc","tags":[]},{"url":"https://git.kernel.org/stable/c/42462b5bb0dec57db7f85d0f77655c737d45754d","tags":[]},{"url":"https://git.kernel.org/stable/c/4eb889649eaf65f4a5727b04ba1c017b7d05bb16","tags":[]},{"url":"https://git.kernel.org/stable/c/863049b4018237d1590cd13b16e9fe9c0faad2c6","tags":[]},{"url":"https://git.kernel.org/stable/c/ebf1555ad2821be06f87a88ffd9a2cab8d2200e1","tags":[]},{"url":"https://git.kernel.org/stable/c/fd3bf32279df98751364b3609eb100a3e42f253b","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}