Re: [Xen-devel] [PATCH] tools: xentoolcore_restrict_all: Do deregistration before close

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Nov 14, 2017 at 12:15:42PM +0000, Ian Jackson wrote:
> Closing the fd before unhooking it from the list runs the risk that a
> concurrent thread calls xentoolcore_restrict_all will operate on the
> old fd value, which might refer to a new fd by then.  So we need to do
> it in the other order.
> 
> Sadly this weakens the guarantee provided by xentoolcore_restrict_all
> slight, but not (I think) in a problematic way.  It would be possible

slightly

> to implement the previous guarantee, but it would involve replacing
> all of the close() calls in all of the individual osdep parts of all
> of the individual libraries with calls to a new function which does
>    dup2("/dev/null", thing->fd);
>    pthread_mutex_lock(&handles_lock);
>    thing->fd = -1;
>    pthread_mutex_unlock(&handles_lock);
>    close(fd);
> which would be terribly tedious.
> 
> Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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