CVE-2026-43385

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> net: Fix rcu_tasks stall in threaded busypoll<br /> <br /> I was debugging a NIC driver when I noticed that when I enable<br /> threaded busypoll, bpftrace hangs when starting up. dmesg showed:<br /> <br /> rcu_tasks_wait_gp: rcu_tasks grace period number 85 (since boot) is 10658 jiffies old.<br /> rcu_tasks_wait_gp: rcu_tasks grace period number 85 (since boot) is 40793 jiffies old.<br /> rcu_tasks_wait_gp: rcu_tasks grace period number 85 (since boot) is 131273 jiffies old.<br /> rcu_tasks_wait_gp: rcu_tasks grace period number 85 (since boot) is 402058 jiffies old.<br /> INFO: rcu_tasks detected stalls on tasks:<br /> 00000000769f52cd: .N nvcsw: 2/2 holdout: 1 idle_cpu: -1/64<br /> task:napi/eth2-8265 state:R running task stack:0 pid:48300 tgid:48300 ppid:2 task_flags:0x208040 flags:0x00004000<br /> Call Trace:<br /> <br /> ? napi_threaded_poll_loop+0x27c/0x2c0<br /> ? __pfx_napi_threaded_poll+0x10/0x10<br /> ? napi_threaded_poll+0x26/0x80<br /> ? kthread+0xfa/0x240<br /> ? __pfx_kthread+0x10/0x10<br /> ? ret_from_fork+0x31/0x50<br /> ? __pfx_kthread+0x10/0x10<br /> ? ret_from_fork_asm+0x1a/0x30<br /> <br /> <br /> The cause is that in threaded busypoll, the main loop is in<br /> napi_threaded_poll rather than napi_threaded_poll_loop, where the<br /> latter rarely iterates more than once within its loop. For<br /> rcu_softirq_qs_periodic inside napi_threaded_poll_loop to report its<br /> qs state, the last_qs must be 100ms behind, and this can&amp;#39;t happen<br /> because napi_threaded_poll_loop rarely iterates in threaded busypoll,<br /> and each time napi_threaded_poll_loop is called last_qs is reset to<br /> latest jiffies.<br /> <br /> This patch changes so that in threaded busypoll, last_qs is saved<br /> in the outer napi_threaded_poll, and whether busy_poll_last_qs<br /> is NULL indicates whether napi_threaded_poll_loop is called for<br /> busypoll. This way last_qs would not reset to latest jiffies on<br /> each invocation of napi_threaded_poll_loop.