Re: [PATCH v3 6/7] util/oslib-posix: Support concurrent os_mem_prealloc() invocation

[David Hildenbrand]

On 28.09.21 18:56, Daniel P. Berrangé wrote:
> On Mon, Aug 16, 2021 at 11:47:38AM +0200, David Hildenbrand wrote:
> > Add a mutex to protect the SIGBUS case, as we cannot mess concurrently
> > with the sigbus handler and we have to manage the global variable
> > sigbus_memset_context. The MADV_POPULATE_WRITE path can run
> > concurrently.
> >
> > Note that page_mutex and page_cond are shared between concurrent
> > invocations, which shouldn't be a problem.
> >
> > This is a preparation for future virtio-mem prealloc code, which will call
> > os_mem_prealloc() asynchronously from an iothread when handling guest
> > requests.
> >
> > Add a comment that messing with the SIGBUS handler is frowned upon and
> > can result in problems we fortunately haven't seen so far. Note that
> > forwarding signals to the already installed SIGBUS handler isn't clean
> > either, as that one might modify the SIGBUS handler again.
>
> Even with the mutex, messing with SIGBUS post-startup still isn't safe
> as we're clashing with SIGBUS usage in softmmu/cpus.c

You raise a valid point, though: this node is stale (there is no such 
comment) and shall be removed :)

Thanks!

--
Thanks,

David / dhildenb