On 08/26/2016 05:55 PM, KarimAllah Ahmed wrote:
> Ever since commit 254d1a3f02eb ("xen/pv-on-hvm kexec: shutdown watches
> from old kernel") using the INTx interrupt from Xen PCI platform device for
> event channel notification would just lockup the guest during bootup.
> postcore_initcall now calls xs_reset_watches which will eventually try to read
> a value from XenStore and will get stuck on read_reply at XenBus forever since
> the platform driver is not probed yet and its INTx interrupt handler is not
> registered yet. That means that the guest can not be notified at this moment
> of
> any pending event channels and none of the per-event handlers will ever be
> invoked (including the XenStore one) and the reply will never be picked up by
> the kernel.
>
> The exact stack where things get stuck during xenbus_init:
>
> -xenbus_init
> -xs_init
> -xs_reset_watches
> -xenbus_scanf
> -xenbus_read
> -xs_single
> -xs_single
> -xs_talkv
>
> Vector callbacks have always been the favourite event notification mechanism
> since their introduction in commit 38e20b07efd5 ("x86/xen: event channels
> delivery on HVM.") and the vector callback feature has always been advertised
> for quite some time by Xen that's why INTx was broken for several years now
> without impacting anyone.
>
> Luckily this also means that event channel notification through INTx is
> basically dead-code which can be safely removed without impacting anybody
> since
> it has been effectively disabled for more than 4 years with nobody complaining
> about it (at least as far as I'm aware of).
>
> This commit removes event channel notification through Xen PCI platform
> device.
>
> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com>
> Cc: David Vrabel <david.vra...@citrix.com>
> Cc: Juergen Gross <jgr...@suse.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: "H. Peter Anvin" <h...@zytor.com>
> Cc: x...@kernel.org
> Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> Cc: Bjorn Helgaas <bhelg...@google.com>
> Cc: Stefano Stabellini <stefano.stabell...@eu.citrix.com>
> Cc: Julien Grall <julien.gr...@citrix.com>
> Cc: Vitaly Kuznetsov <vkuzn...@redhat.com>
> Cc: Paul Gortmaker <paul.gortma...@windriver.com>
> Cc: Ross Lagerwall <ross.lagerw...@citrix.com>
> Cc: xen-de...@lists.xenproject.org
> Cc: linux-ker...@vger.kernel.org
> Cc: linux-...@vger.kernel.org
> Cc: Anthony Liguori <aligu...@amazon.com>
> Signed-off-by: KarimAllah Ahmed <karah...@amazon.de>
Reviewed-by: Boris Ostrovsky <boris.ostrov...@oracle.com>
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