Re: [Qemu-devel] Re: [PATCH] qemu: work around for "posix-aio-compat"

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Oct 09, 2009 at 01:13:12AM +0400, malc wrote:
> On Fri, 9 Oct 2009, malc wrote:
> 
> > On Thu, 8 Oct 2009, Michael S. Tsirkin wrote:
> >
> > > With commit ee3993069ff55fa6f1c64daf1e09963e340db8e4,
> > > "posix-aio-compat: avoid signal race when spawning a thread"
> > > winxp installation on a raw format file fails
> > > during disk format, with a message "your
> > > disk may be damaged".
> > >
> > > This commit moved signal mask from aio thread to creating thread.
> > > It turns out if we keep the mask in aio thread as well, the problem
> > > disappears. It should not be needed, but since this is harmless, let's
> > > keep it around until someone inclined to debug pthread library internals
> > > can check this issue.
> > >
> > > While we are at it, convert sigprocmask to pthread_sigmask
> > > as per posix.
> >
> > Thanks for the work you've put into it, i'll try to see how all of this
> > works on my x86 machine.
> >
> > [..snip..]
> 
> Nope, still can not reproduce... So indeed it appears someone is needed,
> who:
> 
> a. Can reproduce
> b. Cares
> 
> FWIW, in essence sigfillset is this:
> 
> #  define __sigfillset(set) \
>   (__extension__ ({ int __cnt = _SIGSET_NWORDS;                               \
>                     sigset_t *__set = (set);                                  \
>                     while (--__cnt >= 0) __set->__val[__cnt] = ~0UL;          \
>                     0; }))
> 
> So the thing that works for you can be replaced with some dummy loop
> or something,

Exactly. I just did this:

sigset_t xset;

static void *aio_thread(void *unused)
{
    pid_t pid;
    sigset_t set;

    /* block all signals */
    /* Should not be necessary as we should inherit mask
     * from creating thread. However, without this,
     * on FC11, WinXP installation fails during disk format
     * saying disk was damaged. pthread library bug?
     * */
    memset(&set, 0, sizeof set);
    memcpy(&xset, &set, sizeof set);

and it also helps.

> IOW not good enough, we need to understand the problem,
> and as mentioned above, i can not be of any help here, can't repro,
> sorry.
> 
> -- 
> mailto:av1474@comtv.ru