Re: [PATCH] xen/events: close evtchn after mapping cleanup

[Maximilian Heyne]

On Wed, Jan 24, 2024 at 04:31:28PM +0000, Maximilian Heyne wrote:
> shutdown_pirq and startup_pirq are not taking the
> irq_mapping_update_lock because they can't due to lock inversion. Both
> are called with the irq_desc->lock being taking. The lock order,
> however, is first irq_mapping_update_lock and then irq_desc->lock.
> 
> This opens multiple races:
> - shutdown_pirq can be interrupted by a function that allocates an event
>   channel:
> 
>   CPU0                        CPU1
>   shutdown_pirq {
>     xen_evtchn_close(e)
>                               __startup_pirq {
>                                 EVTCHNOP_bind_pirq
>                                   -> returns just freed evtchn e
>                                 set_evtchn_to_irq(e, irq)
>                               }
>     xen_irq_info_cleanup() {
>       set_evtchn_to_irq(e, -1)
>     }
>   }
> 
>   Assume here event channel e refers here to the same event channel
>   number.
>   After this race the evtchn_to_irq mapping for e is invalid (-1).
> 
> - __startup_pirq races with __unbind_from_irq in a similar way. Because
>   __startup_pirq doesn't take irq_mapping_update_lock it can grab the
>   evtchn that __unbind_from_irq is currently freeing and cleaning up. In
>   this case even though the event channel is allocated, its mapping can
>   be unset in evtchn_to_irq.
> 
> The fix is to first cleanup the mappings and then close the event
> channel. In this way, when an event channel gets allocated it's
> potential previous evtchn_to_irq mappings are guaranteed to be unset already.
> This is also the reverse order of the allocation where first the event
> channel is allocated and then the mappings are setup.
> 
> On a 5.10 kernel prior to commit 3fcdaf3d7634 ("xen/events: modify internal
> [un]bind interfaces"), we hit a BUG like the following during probing of NVMe
> devices. The issue is that during nvme_setup_io_queues, pci_free_irq
> is called for every device which results in a call to shutdown_pirq.
> With many nvme devices it's therefore likely to hit this race during
> boot because there will be multiple calls to shutdown_pirq and
> startup_pirq are running potentially in parallel.
> 
>   ------------[ cut here ]------------
>   blkfront: xvda: barrier or flush: disabled; persistent grants: enabled; indirect descriptors: enabled; bounce buffer: enabled
>   kernel BUG at drivers/xen/events/events_base.c:499!
>   invalid opcode: 0000 [#1] SMP PTI
>   CPU: 44 PID: 375 Comm: kworker/u257:23 Not tainted 5.10.201-191.748.amzn2.x86_64 #1
>   Hardware name: Xen HVM domU, BIOS 4.11.amazon 08/24/2006
>   Workqueue: nvme-reset-wq nvme_reset_work
>   RIP: 0010:bind_evtchn_to_cpu+0xdf/0xf0
>   Code: 5d 41 5e c3 cc cc cc cc 44 89 f7 e8 2b 55 ad ff 49 89 c5 48 85 c0 0f 84 64 ff ff ff 4c 8b 68 30 41 83 fe ff 0f 85 60 ff ff ff <0f> 0b 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 0f 1f 44 00 00
>   RSP: 0000:ffffc9000d533b08 EFLAGS: 00010046
>   RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000006
>   RDX: 0000000000000028 RSI: 00000000ffffffff RDI: 00000000ffffffff
>   RBP: ffff888107419680 R08: 0000000000000000 R09: ffffffff82d72b00
>   R10: 0000000000000000 R11: 0000000000000000 R12: 00000000000001ed
>   R13: 0000000000000000 R14: 00000000ffffffff R15: 0000000000000002
>   FS:  0000000000000000(0000) GS:ffff88bc8b500000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 0000000000000000 CR3: 0000000002610001 CR4: 00000000001706e0
>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>   Call Trace:
>    ? show_trace_log_lvl+0x1c1/0x2d9
>    ? show_trace_log_lvl+0x1c1/0x2d9
>    ? set_affinity_irq+0xdc/0x1c0
>    ? __die_body.cold+0x8/0xd
>    ? die+0x2b/0x50
>    ? do_trap+0x90/0x110
>    ? bind_evtchn_to_cpu+0xdf/0xf0
>    ? do_error_trap+0x65/0x80
>    ? bind_evtchn_to_cpu+0xdf/0xf0
>    ? exc_invalid_op+0x4e/0x70
>    ? bind_evtchn_to_cpu+0xdf/0xf0
>    ? asm_exc_invalid_op+0x12/0x20
>    ? bind_evtchn_to_cpu+0xdf/0xf0
>    ? bind_evtchn_to_cpu+0xc5/0xf0
>    set_affinity_irq+0xdc/0x1c0
>    irq_do_set_affinity+0x1d7/0x1f0
>    irq_setup_affinity+0xd6/0x1a0
>    irq_startup+0x8a/0xf0
>    __setup_irq+0x639/0x6d0
>    ? nvme_suspend+0x150/0x150
>    request_threaded_irq+0x10c/0x180
>    ? nvme_suspend+0x150/0x150
>    pci_request_irq+0xa8/0xf0
>    ? __blk_mq_free_request+0x74/0xa0
>    queue_request_irq+0x6f/0x80
>    nvme_create_queue+0x1af/0x200
>    nvme_create_io_queues+0xbd/0xf0
>    nvme_setup_io_queues+0x246/0x320
>    ? nvme_irq_check+0x30/0x30
>    nvme_reset_work+0x1c8/0x400
>    process_one_work+0x1b0/0x350
>    worker_thread+0x49/0x310
>    ? process_one_work+0x350/0x350
>    kthread+0x11b/0x140
>    ? __kthread_bind_mask+0x60/0x60
>    ret_from_fork+0x22/0x30
>   Modules linked in:
>   ---[ end trace a11715de1eee1873 ]---
> 
> Fixes: d46a78b05c0e ("xen: implement pirq type event channels")
> Cc: stable@xxxxxxxxxxxxxxx
> Co-debugged-by: Andrew Panyakin <apanyaki@xxxxxxxxxx>
> Signed-off-by: Maximilian Heyne <mheyne@xxxxxxxxx>

Friendly ping. Did anyone find time to look at this?



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