nfsd: fix layout fence worker double-reference race

Overview

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix layout fence worker double-reference race

The workqueue core clears WORK_STRUCT_PENDING before the callback is invoked, so delayed_work_pending() in lm_breaker_timedout() can return false while the fence worker is already running. This lets the breaker take a duplicate sc_count reference and schedule a new worker that coalesces with the in-progress one. The extra reference is never put, leaking the layout stateid.

Replace the racy delayed_work_pending() check with an ls_fence_inflight boolean set atomically with refcount_inc_not_zero() under ls_lock, and cleared under ls_lock before the final nfs4_put_stid() on the dispose path; the retry path intentionally retains it. Remove the self-rearm mod_delayed_work() at the top of the worker.

Affected

• Linux >= f52792f484ba2316853736856dde19b7e7458861 < a278d361e0e8f242211891193d56483a7a9f47a8
• Linux >= f52792f484ba2316853736856dde19b7e7458861 < 8580571227451384399b3fa53fcde19848c48e5a
• Linux 7.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Low · affected: Red Hat Enterprise Linux 10 · no fix planned: Red Hat Enterprise Linux 10 · updated 2026-10-05 · vex