CVE-2024-46797: In the Linux kernel, the following vulnerability has been resolved:  powerpc/qspinlock: Fix deadlock in MCS queue  If an interrupt occurs in queued_spin_lock_slowpath() after we increment qnodesp->count and before node->lock is initialized, another CPU might see stale lock values in get_tail_qnode(). If the stale lock value happens to match the lock on that CPU, then we write to the "next" pointer of the wrong qnode. This causes a deadlock as the former CPU, once it becomes the head of the MCS queue, will spin indefinitely until it's "next" pointer is set by its successor in the queue.  Running stress-ng on a 16 core (16EC/16VP) shared LPAR, results in occasional lockups similar to the following:     $ stress-ng --all 128 --vm-bytes 80% --aggressive \                --maximize --oomable --verify  --syslog \                --metrics  --times  --timeout 5m     watchdog: CPU 15 Hard LOCKUP    ......    NIP [c0000000000b78f4] queued_spin_lock_slowpath+0x1184/0x1490    LR [c000000001037c5c] _raw_spin_lock+0x6c/0x90    Call Trace:     0xc000002cfffa3bf0 (unreliable)     _raw_spin_lock+0x6c/0x90     raw_spin_rq_lock_nested.part.135+0x4c/0xd0     sched_ttwu_pending+0x60/0x1f0     __flush_smp_call_function_queue+0x1dc/0x670     smp_ipi_demux_relaxed+0xa4/0x100     xive_muxed_ipi_action+0x20/0x40     __handle_irq_event_percpu+0x80/0x240     handle_irq_event_percpu+0x2c/0x80     handle_percpu_irq+0x84/0xd0     generic_handle_irq+0x54/0x80     __do_irq+0xac/0x210     __do_IRQ+0x74/0xd0     0x0     do_IRQ+0x8c/0x170     hardware_interrupt_common_virt+0x29c/0x2a0    --- interrupt: 500 at queued_spin_lock_slowpath+0x4b8/0x1490    ......    NIP [c0000000000b6c28] queued_spin_lock_slowpath+0x4b8/0x1490    LR [c000000001037c5c] _raw_spin_lock+0x6c/0x90    --- interrupt: 500     0xc0000029c1a41d00 (unreliable)     _raw_spin_lock+0x6c/0x90     futex_wake+0x100/0x260     do_futex+0x21c/0x2a0     sys_futex+0x98/0x270     system_call_exception+0x14c/0x2f0     system_call_vectored_common+0x15c/0x2ec  The following code flow illustrates how the deadlock occurs. For the sake of brevity, assume that both locks (A and B) are contended and we call the queued_spin_lock_slowpath() function.          CPU0                                   CPU1         ----                                   ----   spin_lock_irqsave(A)                          |   spin_unlock_irqrestore(A)                     |     spin_lock(B)                                |          |                                      |          ▼                                      |    id = qnodesp->count++;                       |   (Note that nodes[0].lock == A)                |          |                                      |          ▼                                      |       Interrupt                                 |   (happens before "nodes[0].lock = B")          |          |                                      |          ▼                                      |   spin_lock_irqsave(A)                          |          |                                      |          ▼                                      |    id = qnodesp->count++                        |    nodes[1].lock = A                            |          |                                      |          ▼                                      |   Tail of MCS queue                             |          |                             spin_lock_irqsave(A)          ▼                                      |   Head of MCS queue                             ▼          |                             CPU0 is previous tail          ▼                                      |    Spin indefinitely                            ▼   (until "nodes[1].next != NULL")      prev = get_tail_qnode(A, CPU0)                                                 |                                                 ▼                                        prev == &qnodes[CPU0].nodes[0]                                      (as qnodes ---truncated---