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

[George Dunlap <george.dunlap@citrix.com>]

On 25/09/15 08:46, Dario Faggioli wrote:
> especially if that is also from a different cpupool than the
> processor of the vCPU that triggered the tickling.
> 
> In fact, it is possible that we get as far as calling vcpu_unblock()-->
> vcpu_wake()-->csched_vcpu_wake()-->__runq_tickle() for the vCPU 'vc',
> but all while running on a pCPU that is different from 'vc->processor'.
> 
> 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
> 
> In this case, pCPU 7 is not in Pool-0, while the (Dom0's) vCPU being
> woken is. pCPU's 7 pool has a different scheduler than credit, but it
> is, however, right from pCPU 7 that we are waking the Dom0's vCPUs.
> Therefore, the current code tries to access csched_balance_mask for
> pCPU 7, but that is not defined, and hence the Oops.
> 
> (Note that, in case the two pools run the same scheduler we see no
> Oops, but things are still conceptually wrong.)
> 
> Cure things by making the csched_balance_mask macro accept a
> parameter for fetching a specific pCPU's mask (instead than always
> using smp_processor_id()).
> 
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
> Reviewed-by: Juergen Gross <jgross@suse.com>

Looks good!

Reviewed-by: George Dunlap <george.dunlap@citrix.com>