CVE-2026-89549sunrpc: route to a populated pool in svc_pool_for_cpu()

Official description

In the Linux kernel, the following vulnerability has been resolved: sunrpc: route to a populated pool in svc_pool_for_cpu() svc_set_num_threads() spreads the requested threads evenly across the service's pools (base = nrservs / sv_nrpools). When a service runs fewer threads than it has pools -- e.g. an nfsd configured with fewer threads than the host has NUMA nodes while running in "pernode" or "percpu" mode -- the trailing pools are left with no threads at all. svc_xprt_enqueue() selects a pool from the CPU servicing the transport, queues the transport on that pool's sp_xprts, and only wakes a thread from the same pool. Each thread services exclusively its own pool, so a transport that lands on a threadless pool is enqueued on sp_xprts and never picked up: the connection hangs indefinitely. Have svc_pool_for_cpu() skip pools that currently have no threads, falling back to the next populated pool. This trades NUMA locality for a guarantee that the work is actually serviced. sp_nrthreads is only updated under the service mutex; the lockless read here is a best-effort routing hint, so annotate it with data_race().

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/9accc25e5af0bac8479f6054e674b2c593c45281
• https://git.kernel.org/stable/c/6f66d38e2a6c78d48723ea17ad86135ec80ca24b
• https://git.kernel.org/stable/c/d79d7b9e8acbb53e2d60f6b24afc13e2f15e691f
• https://git.kernel.org/stable/c/edb20e8c03aebacb409968c99d046f509c6c485a
• https://git.kernel.org/stable/c/011479cf9a7657d4a3e7cc42a784ac63df594170
• https://git.kernel.org/stable/c/9d04d64ad192439835ed9884d767353061c3ed6f
• https://git.kernel.org/stable/c/8f766d2d0b4dabf54f8b35812df2b4f481d13316
• https://git.kernel.org/stable/c/f6310491c4cdb88af73aa551ec9df1f10a90c709