Re: [PATCH v3 06/10] monitor: release the lock before calling close()

[Marc-André Lureau]

Hi

On Tue, Feb 14, 2023 at 5:34 PM Markus Armbruster <armbru@redhat.com> wrote:
>
> marcandre.lureau@redhat.com writes:
>
> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> >
> > As per comment, presumably to avoid syscall in critical section.
> >
> > Fixes: 0210c3b39bef08 ("monitor: Use LOCK_GUARD macros")
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> >  monitor/fds.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/monitor/fds.c b/monitor/fds.c
> > index 26b39a0ce6..03c5e97c35 100644
> > --- a/monitor/fds.c
> > +++ b/monitor/fds.c
> > @@ -80,7 +80,7 @@ void qmp_getfd(const char *fdname, Error **errp)
> >          return;
> >      }
> >
> > -    QEMU_LOCK_GUARD(&cur_mon->mon_lock);
> > +    qemu_mutex_lock(&cur_mon->mon_lock);
> >      QLIST_FOREACH(monfd, &cur_mon->fds, next) {
> >          if (strcmp(monfd->name, fdname) != 0) {
> >              continue;
> > @@ -88,6 +88,7 @@ void qmp_getfd(const char *fdname, Error **errp)
> >
> >          tmp_fd = monfd->fd;
> >          monfd->fd = fd;
> > +        qemu_mutex_unlock(&cur_mon->mon_lock);
> >          /* Make sure close() is outside critical section */
> >          close(tmp_fd);
> >          return;
> > @@ -98,6 +99,7 @@ void qmp_getfd(const char *fdname, Error **errp)
> >      monfd->fd = fd;
> >
> >      QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
> > +    qemu_mutex_unlock(&cur_mon->mon_lock);
> >  }
> >
> >  void qmp_closefd(const char *fdname, Error **errp)
>
> This confused me.  I think I understand now, but let's double-check.
>
> You're reverting commit 0210c3b39bef08 for qmp_getfd() because it
> extended the criticial section beyond the close(), invalidating the
> comment.  Correct?

Correct

>
> Did it actually break anything?

Not that I know of (David admitted over IRC that this was not intended)

-- 
Marc-André Lureau