Re: [Xen-devel] [PATCH v2] xen: credit1: fix tickling when it happens from a remote pCPU

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

Hey Wei,

On Fri, 2015-09-25 at 09:46 +0200, Dario Faggioli wrote:

> For instance, this can happen when an HVM domain runs in a cpupool,
> with a different scheduler than the default one, and issues IOREQs
> to Dom0, running in Pool-0 with the default scheduler.
> In fact, right in this case, the following crash can be observed:

> (XEN) ----[ Xen-4.7-unstable  x86_64  debug=y  Tainted:    C ]----
> (XEN) CPU:    7
> (XEN) RIP:    e008:[<ffff82d0801230de>] __runq_tickle+0x18f/0x430
> (XEN) RFLAGS: 0000000000010086   CONTEXT: hypervisor (d1v0)
> (XEN) rax: 0000000000000001   rbx: ffff8303184fee00   rcx:
> 0000000000000000
> (XEN) ... ... ...
> (XEN) Xen stack trace from rsp=ffff83031fa57a08:
> (XEN)    ffff82d0801fe664 ffff82d08033c820 0000000100000002
> 0000000a00000001
> (XEN)    0000000000006831 0000000000000000 0000000000000000
> 0000000000000000
> (XEN) ... ... ...
> (XEN) Xen call trace:
> (XEN)    [<ffff82d0801230de>] __runq_tickle+0x18f/0x430
> (XEN)    [<ffff82d08012348a>] csched_vcpu_wake+0x10b/0x110
> (XEN)    [<ffff82d08012b421>] vcpu_wake+0x20a/0x3ce
> (XEN)    [<ffff82d08012b91c>] vcpu_unblock+0x4b/0x4e
> (XEN)    [<ffff82d080167bd0>] vcpu_kick+0x17/0x61
> (XEN)    [<ffff82d080167c46>] vcpu_mark_events_pending+0x2c/0x2f
> (XEN)    [<ffff82d08010ac35>] evtchn_fifo_set_pending+0x381/0x3f6
> (XEN)    [<ffff82d08010a0f6>] notify_via_xen_event_channel+0xc9/0xd6
> (XEN)    [<ffff82d0801c29ed>] hvm_send_ioreq+0x3e9/0x441
> (XEN)    [<ffff82d0801bba7d>] hvmemul_do_io+0x23f/0x2d2
> (XEN)    [<ffff82d0801bbb43>] hvmemul_do_io_buffer+0x33/0x64
> (XEN)    [<ffff82d0801bc92b>] hvmemul_do_pio_buffer+0x35/0x37
> (XEN)    [<ffff82d0801cc49f>] handle_pio+0x58/0x14c
> (XEN)    [<ffff82d0801eabcb>] vmx_vmexit_handler+0x16b3/0x1bea
> (XEN)    [<ffff82d0801efd21>] vmx_asm_vmexit_handler+0x41/0xc0
> 
This patch is a bugfix, so I think it should be included in 4.6.

I'm able to trigger the above Oops pretty reliably by running an HVM
guest in a cpupool that has a scheduler different than Credit (by,
e.g., starting some load in the guest itself, or even just simply doing
`xl shutdown' on it).

It may not be the most common of the configurations, but I think it's
worth.

Thanks and Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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