[Xen-devel] [PATCH 0/2] Re: libvirtd live-locking on CTX_LOCK when doing 'virsh <domid> save /tmp/blah' with guest corrupting memory (on purpose).

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Konrad Rzeszutek Wilk writes ("libvirtd live-locking on CTX_LOCK when doing 
'virsh <domid> save /tmp/blah' with guest corrupting memory (on purpose)."):
> It looks like thread #10 is blocking in libxl_read_exactly waiting
> for 'libxl-save-helper'. Said application (see below) has dispatched
> an message through helper_getreply and is blocking on __read_nocancel.

This is not supposed to block.

helper_stdout_readable assumes that the fd is actually readable.
However, for complicated reasons it can happen in a multithreaded
program that the fd was _reviously_ readable and is now no longer.

This was not clearly documented in the internal API documentation.

I have produced what I think are two patches that will fix this.  I
have compiled them but I haven't tested them.  Konrad, are you able to
check whether they fix your bug ?

If they do they are candidates for backporting.

Thanks,
Ian.

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