CVE-2023-52587: In the Linux kernel, the following vulnerability has been resolved:  IB/ipoib: Fix mcast list locking  Releasing the `priv->lock` while iterating the `priv->multicast_list` in `ipoib_mcast_join_task()` opens a window for `ipoib_mcast_dev_flush()` to remove the items while in the middle of iteration. If the mcast is removed while the lock was dropped, the for loop spins forever resulting in a hard lockup (as was reported on RHEL 4.18.0-372.75.1.el8_6 kernel):      Task A (kworker/u72:2 below)       | Task B (kworker/u72:0 below)     -----------------------------------+-----------------------------------     ipoib_mcast_join_task(work)        | ipoib_ib_dev_flush_light(work)       spin_lock_irq(&priv->lock)       | __ipoib_ib_dev_flush(priv, ...)       list_for_each_entry(mcast,       | ipoib_mcast_dev_flush(dev = priv->dev)           &priv->multicast_list, list) |         ipoib_mcast_join(dev, mcast)   |           spin_unlock_irq(&priv->lock) |                                        |   spin_lock_irqsave(&priv->lock, flags)                                        |   list_for_each_entry_safe(mcast, tmcast,                                        |                  &priv->multicast_list, list)                                        |     list_del(&mcast->list);                                        |     list_add_tail(&mcast->list, &remove_list)                                        |   spin_unlock_irqrestore(&priv->lock, flags)           spin_lock_irq(&priv->lock)   |                                        |   ipoib_mcast_remove_list(&remove_list)    (Here, `mcast` is no longer on the  |     list_for_each_entry_safe(mcast, tmcast,     `priv->multicast_list` and we keep |                            remove_list, list)     spinning on the `remove_list` of   |  >>>  wait_for_completion(&mcast->done)     the other thread which is blocked  |     and the list is still valid on     |     it's stack.)  Fix this by keeping the lock held and changing to GFP_ATOMIC to prevent eventual sleeps. Unfortunately we could not reproduce the lockup and confirm this fix but based on the code review I think this fix should address such lockups.  crash> bc 31 PID: 747      TASK: ff1c6a1a007e8000  CPU: 31   COMMAND: "kworker/u72:2" --     [exception RIP: ipoib_mcast_join_task+0x1b1]     RIP: ffffffffc0944ac1  RSP: ff646f199a8c7e00  RFLAGS: 00000002     RAX: 0000000000000000  RBX: ff1c6a1a04dc82f8  RCX: 0000000000000000                                   work (&priv->mcast_task{,.work})     RDX: ff1c6a192d60ac68  RSI: 0000000000000286  RDI: ff1c6a1a04dc8000            &mcast->list     RBP: ff646f199a8c7e90   R8: ff1c699980019420   R9: ff1c6a1920c9a000     R10: ff646f199a8c7e00  R11: ff1c6a191a7d9800  R12: ff1c6a192d60ac00                                                          mcast     R13: ff1c6a1d82200000  R14: ff1c6a1a04dc8000  R15: ff1c6a1a04dc82d8            dev                    priv (&priv->lock)     &priv->multicast_list (aka head)     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018 --- <NMI exception stack> ---  #5 [ff646f199a8c7e00] ipoib_mcast_join_task+0x1b1 at ffffffffc0944ac1 [ib_ipoib]  #6 [ff646f199a8c7e98] process_one_work+0x1a7 at ffffffff9bf10967  crash> rx ff646f199a8c7e68 ff646f199a8c7e68:  ff1c6a1a04dc82f8 <<< work = &priv->mcast_task.work  crash> list -hO ipoib_dev_priv.multicast_list ff1c6a1a04dc8000 (empty)  crash> ipoib_dev_priv.mcast_task.work.func,mcast_mutex.owner.counter ff1c6a1a04dc8000   mcast_task.work.func = 0xffffffffc0944910 <ipoib_mcast_join_task>,   mcast_mutex.owner.counter = 0xff1c69998efec000  crash> b 8 PID: 8        TASK: ff1c69998efec000  CPU: 33   COMMAND: "kworker/u72:0" --  #3 [ff646f1980153d50] wait_for_completion+0x96 at ffffffff9c7d7646  #4 [ff646f1980153d90] ipoib_mcast_remove_list+0x56 at ffffffffc0944dc6 [ib_ipoib]  #5 [ff646f1980153de8] ipoib_mcast_dev_flush+0x1a7 at ffffffffc09455a7 [ib_ipoib]  #6 [ff646f1980153e58] __ipoib_ib_dev_flush+0x1a4 at ffffffffc09431a4 [ib_ipoib]  #7 [ff ---truncated---