CVE-2026-64211

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> srcu: Don&amp;#39;t queue workqueue handlers to never-online CPUs<br /> <br /> While an srcu_struct structure is in the midst of switching from CPU-0<br /> to all-CPUs state, it can attempt to invoke callbacks for CPUs that<br /> have never been online. Worse yet, it can attempt in invoke callbacks<br /> for CPUs that never will be online, even including imaginary CPUs not in<br /> cpu_possible_mask. This can cause hangs on s390, which is not set up to<br /> deal with workqueue handlers being scheduled on such CPUs. This commit<br /> therefore causes Tree SRCU to refrain from queueing workqueue handlers<br /> on CPUs that have not yet (and might never) come online.<br /> <br /> Because callbacks are not invoked on CPUs that have not been<br /> online, it is an error to invoke call_srcu(), synchronize_srcu(), or<br /> synchronize_srcu_expedited() on a CPU that is not yet fully online.<br /> However, it turns out to be less code to redirect the callbacks<br /> from too-early invocations of call_srcu() than to warn about such<br /> invocations. This commit therefore also redirects callbacks queued on<br /> not-yet-fully-online CPUs to the boot CPU.