Re: [Xen-devel] [PATCH] Revert xen: dont fiddle with event channel masking in suspend/resume

[Juergen Gross <jgross@xxxxxxxx>]

On 20/04/18 01:04, Anchal Agarwal wrote:
> 
> Hello,
> 
> This patch reverts commit e91b2b1194335ca83d8a40fa4e0efd480bf2babe.
> evtchn are supposed to be masked during resume by irq subsytem 
> however, they are not. This causes special interrupts like PV 
> spinlock to cause kernel BUG() as it expects the IRQ to be 
> masked. This causes instances that are live migrated successfully 
> to crash after few minutes.
> 
> Live Migration uses suspend resume and when xen_irq_resume is invoked, 
> I saw event channels are not masked. Hence, I reverted this
> commit to make LM work. Feelings? Recommendations? Things I missed?

The commit you are reverting was meant to repair suspend/resume handling
for Xen. Instead of just reverting it the correct thing to do would be
to find the reason why some event channels are not being masked and
address that issue.

See https://lists.xen.org/archives/html/xen-devel/2017-07/msg00898.html


Juergen

> 
> One such stack:
>  ------------[ cut here ]------------
>  kernel BUG at arch/x86/xen/spinlock.c:75!
>  CPU: 0 PID: 675 Comm: kauditd Not tainted 4.14.20-48.30.amzn2.x86_64 #1
>  Hardware name: Xen HVM domU, BIOS 4.2.amazon 08/24/2006
>  task: ffff880205eedac0 task.stack: ffffc90000e4c000
>  RIP: 0010:dummy_handler+0x0/0x10
>  RSP: 0018:ffff880207203eb8 EFLAGS: 00010046
>  RAX: ffffffff81027f10 RBX: ffff880206ce1b00 RCX: 0000000000000035
>  RDX: ffffffff81a81560 RSI: 0000000000000000 RDI: 0000000000000035
>  RBP: 0000000000000035 R08: ffff880206800248 R09: ffff880206d03600
>  R10: 0000000000000000 R11: 0000000000000040 R12: 0000000000000000
>  R13: ffff880207203f04 R14: 0000000000000000 R15: 0000000000000000
>  FS:  0000000000000000(0000) GS:ffff880207200000(0000) 
>  knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000561cc8dbd2d0 CR3: 0000000001e0a001 CR4: 00000000001606f0
>  Call Trace:
>   <IRQ>
>   __handle_irq_event_percpu+0x40/0x190
>   handle_irq_event_percpu+0x30/0x70
>   handle_percpu_irq+0x37/0x50
>   generic_handle_irq+0x24/0x30
>   evtchn_2l_handle_events+0x162/0x280
>   __xen_evtchn_do_upcall+0x42/0x80
>   xen_evtchn_do_upcall+0x27/0x40
>   xen_hvm_callback_vector+0x98/0xa0
>   </IRQ>
>  RIP: 0010:finish_task_switch+0x7b/0x200
>  RSP: 0018:ffffc90000e4fe08 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff0c
>  RAX: 0000000000000001 RBX: ffff880205eedac0 RCX: 0000000000000000
>  RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8802072211c0
>  RBP: ffffc90000e4fe30 R08: 0000003876060000 R09: 0000000000000000
>  R10: 0000000000000000 R11: 0000000000000040 R12: ffff8802072211c0
>  R13: ffffffff81e12480 R14: ffff880202e54c00 R15: 0000000000000000
>   ? finish_task_switch+0x74/0x200
>   __schedule+0x29c/0x8a0
>   ? __wake_up_common_lock+0x89/0xc0
>   ? kauditd_send_multicast_skb+0x90/0x90
>   schedule+0x28/0x80
>   kauditd_thread+0x177/0x220
>   ? finish_wait+0x80/0x80
>   ? auditd_reset+0x90/0x90
>   kthread+0x11a/0x130
>   ? kthread_create_on_node+0x70/0x70
>   ? call_usermodehelper_exec_async+0x12a/0x160
>   ret_from_fork+0x35/0x40
>   RIP: dummy_handler+0x0/0x10 RSP: ffff880207203eb8
> 
> Signed-off-by: Anchal Agarwal <anchalag@xxxxxxxxxx>
> Signed-off-by: Eduardo Valentin <eduval@xxxxxxxxxx>
> Reviewed-by: Frank van der Linden <fllinden@xxxxxxxxxx>
> Reviewed-by: Alakesh Haloi <alakeshh@xxxxxxxxxx>
> Reviewed-by: Vallish Vaidyeshwara <vallish@xxxxxxxxxx>
> 
> ---
>  drivers/xen/events/events_base.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/xen/events/events_base.c 
> b/drivers/xen/events/events_base.c
> index bc03f1a6ad1b..ae71cab207f7 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -343,6 +343,14 @@ static void bind_evtchn_to_cpu(unsigned int chn, 
> unsigned int cpu)
>       info->cpu = cpu;
>  }
>  
> +static void xen_evtchn_mask_all(void)
> +{
> +     unsigned int evtchn;
> +
> +     for (evtchn = 0; evtchn < xen_evtchn_nr_channels(); evtchn++)
> +             mask_evtchn(evtchn);
> +}
> +
>  /**
>   * notify_remote_via_irq - send event to remote end of event channel via irq
>   * @irq: irq of event channel to send event to
> @@ -1565,6 +1573,7 @@ void xen_irq_resume(void)
>       struct irq_info *info;
>  
>       /* New event-channel space is not 'live' yet. */
> +     xen_evtchn_mask_all();
>       xen_evtchn_resume();
>  
>       /* No IRQ <-> event-channel mappings. */
> @@ -1682,7 +1691,6 @@ module_param(fifo_events, bool, 0);
>  void __init xen_init_IRQ(void)
>  {
>       int ret = -EINVAL;
> -     unsigned int evtchn;
>  
>       if (fifo_events)
>               ret = xen_evtchn_fifo_init();
> @@ -1694,8 +1702,7 @@ void __init xen_init_IRQ(void)
>       BUG_ON(!evtchn_to_irq);
>  
>       /* No event channels are 'live' right now. */
> -     for (evtchn = 0; evtchn < xen_evtchn_nr_channels(); evtchn++)
> -             mask_evtchn(evtchn);
> +     xen_evtchn_mask_all();
>  
>       pirq_needs_eoi = pirq_needs_eoi_flag;
>  
> 


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