Re: [Xen-devel] [PATCH 1/2] libxl: fix reentrancy hazard in fd event processing

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Campbell writes ("Re: [PATCH 1/2] libxl: fix reentrancy hazard in fd event 
processing"):
> On Fri, 2012-07-20 at 19:18 +0100, Ian Jackson wrote:
...
> >   Program terminated with signal 11, Segmentation fault.
> >   #0  0x00007f7ff743131b in afterpoll_check_fd (poller=<optimized out>, 
> > fds=0x7f7ff7b241c0, nfds=7, fd=-1, events=1)
> >       at libxl_event.c:856
> >   856             if (fds[slot].fd != fd)
> 
> Has Roger or you tested this now?

I still haven't tested the new version I'm afraid.

> It looks plausible to me.

:-).

> > diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> > index 2781398..e938660 100644
> > --- a/tools/libxl/libxl_internal.h
> > +++ b/tools/libxl/libxl_internal.h
> > @@ -272,7 +272,7 @@ struct libxl__poller {
> >      int fd_polls_allocd;
> >  
> >      int fd_rindices_allocd;
> > -    int (*fd_rindices)[3]; /* see libxl_osevent_beforepoll */
> > +    int (*fd_rindices)[3]; /* see libxl_event.c:beforepoll_internal */
> 
> do you mean afterpoll here?

No.  I mean this comment:

    /*
     * In order to be able to efficiently find the libxl__ev_fd for a
     * struct poll during _afterpoll, we maintain a shadow data
     * structure in CTX->fd_rindices: each fd corresponds to a slot in
     * fd_rindices, and each element in the rindices is three indices
     * into the fd array (for POLLIN, POLLPRI and POLLOUT).
     */

which is halfway down beforepoll_internal.

Ian.

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