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ixgbe: Add locking to prevent panic when setting sriov_numvfs to zero

Ken Cox requested to merge kencox/centos-stream-9:RHEL-9.1-ixgbevf.bz2109871.00.mycommits into main 
Bugzilla: http://bugzilla.redhat.com/2109871
Tested: local testing using reproducer in commit log

    commit 1e53834ce541d4fe271cdcca7703e50be0a44f8a
    Author: Piotr Skajewski <piotrx.skajewski@intel.com>
    Date:   Fri Jul 15 14:44:56 2022 -0700
    
        ixgbe: Add locking to prevent panic when setting sriov_numvfs to zero
    
        It is possible to disable VFs while the PF driver is processing requests
        from the VF driver.  This can result in a panic.
    
        BUG: unable to handle kernel paging request at 000000000000106c
        PGD 0 P4D 0
        Oops: 0000 [#1] SMP NOPTI
        CPU: 8 PID: 0 Comm: swapper/8 Kdump: loaded Tainted: G I      --------- -
        Hardware name: Dell Inc. PowerEdge R740/06WXJT, BIOS 2.8.2 08/27/2020
        RIP: 0010:ixgbe_msg_task+0x4c8/0x1690 [ixgbe]
        Code: 00 00 48 8d 04 40 48 c1 e0 05 89 7c 24 24 89 fd 48 89 44 24 10 83 ff
        01 0f 84 b8 04 00 00 4c 8b 64 24 10 4d 03 a5 48 22 00 00 <41> 80 7c 24 4c
        00 0f 84 8a 03 00 00 0f b7 c7 83 f8 08 0f 84 8f 0a
        RSP: 0018:ffffb337869f8df8 EFLAGS: 00010002
        RAX: 0000000000001020 RBX: 0000000000000000 RCX: 000000000000002b
        RDX: 0000000000000002 RSI: 0000000000000008 RDI: 0000000000000006
        RBP: 0000000000000006 R08: 0000000000000002 R09: 0000000000029780
        R10: 00006957d8f42832 R11: 0000000000000000 R12: 0000000000001020
        R13: ffff8a00e8978ac0 R14: 000000000000002b R15: ffff8a00e8979c80
        FS:  0000000000000000(0000) GS:ffff8a07dfd00000(0000) knlGS:00000000000000
        CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
        CR2: 000000000000106c CR3: 0000000063e10004 CR4: 00000000007726e0
        DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
        DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
        PKRU: 55555554
        Call Trace:
         <IRQ>
         ? ttwu_do_wakeup+0x19/0x140
         ? try_to_wake_up+0x1cd/0x550
         ? ixgbevf_update_xcast_mode+0x71/0xc0 [ixgbevf]
         ixgbe_msix_other+0x17e/0x310 [ixgbe]
         __handle_irq_event_percpu+0x40/0x180
         handle_irq_event_percpu+0x30/0x80
         handle_irq_event+0x36/0x53
         handle_edge_irq+0x82/0x190
         handle_irq+0x1c/0x30
         do_IRQ+0x49/0xd0
         common_interrupt+0xf/0xf
    
        This can be eventually be reproduced with the following script:
    
        while :
        do
            echo 63 > /sys/class/net/<devname>/device/sriov_numvfs
            sleep 1
            echo 0 > /sys/class/net/<devname>/device/sriov_numvfs
            sleep 1
        done
    
        Add lock when disabling SR-IOV to prevent process VF mailbox communication.
    
        Fixes: d773d1310625 ("ixgbe: Fix memory leak when SR-IOV VFs are direct assigned")
        Signed-off-by: Piotr Skajewski <piotrx.skajewski@intel.com>
        Tested-by: Marek Szlosek <marek.szlosek@intel.com>
        Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
        Link: https://lore.kernel.org/r/20220715214456.2968711-1-anthony.l.nguyen@intel.com
        Signed-off-by: Jakub Kicinski <kuba@kernel.org>





Signed-off-by: Ken Cox <jkc@redhat.com>
```
Edited by Ken Cox

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