On Sat, Jan 15, 2022 at 2:49 AM Alex Bennée <[email protected]> wrote:
> > Peter Maydell <[email protected]> writes: > > > In linux-user/signal.c we have two FIXME comments claiming that > > parts of the signal-handling code are not threadsafe. These are > > very old, as they were first introduced in commit 624f7979058 > > in 2008. Since then we've radically overhauled the signal-handling > > logic, while carefully preserving these FIXME comments. > > > > It's unclear exactly what thread-safety issue the original > > author was trying to point out -- the relevant data structures > > are in the TaskStruct, which makes them per-thread and only > > operated on by that thread. The old code at the time of that > > commit did have various races involving signal handlers being > > invoked at awkward times; possibly this was what was meant. > > > > Delete these FIXME comments: > > * they were written at a time when the way we handled > > signals was completely different > > * the code today appears to us to not have thread-safety issues > > * nobody knows what the problem the comments were trying to > > point out was > > so they are serving no useful purpose for us today. > > > > Signed-off-by: Peter Maydell <[email protected]> > > --- > > Marked "RFC" because I'm a bit uneasy with deleting FIXMEs > > simply because I can't personally figure out why they're > > there. This patch is more to start a discussion to see > > if anybody does understand the issue -- in which case we > > can instead augment the comments to describe it. > > --- > > linux-user/signal.c | 2 -- > > 1 file changed, 2 deletions(-) > > > diff --git a/linux-user/signal.c b/linux-user/signal.c > > index 32854bb3752..e7410776e21 100644 > > --- a/linux-user/signal.c > > +++ b/linux-user/signal.c > > @@ -1001,7 +1001,6 @@ int do_sigaction(int sig, const struct > target_sigaction *act, > > oact->sa_mask = k->sa_mask; > > } > > if (act) { > > - /* FIXME: This is not threadsafe. */ > > __get_user(k->_sa_handler, &act->_sa_handler); > > __get_user(k->sa_flags, &act->sa_flags); > > #ifdef TARGET_ARCH_HAS_SA_RESTORER > > @@ -1151,7 +1150,6 @@ void process_pending_signals(CPUArchState *cpu_env) > > sigset_t *blocked_set; > > > > while (qatomic_read(&ts->signal_pending)) { > > - /* FIXME: This is not threadsafe. */ > > sigfillset(&set); > > sigprocmask(SIG_SETMASK, &set, 0); > > Looking at the history those FIXMEs could have been for code that they > where attached to. Could the thread safety be about reading the > sigaction stuff? I would have though sigaction updates where atomic by > virtue of the syscall to set them... > > Anyway looks old to me: > > Reviewed-by: Alex Bennée <[email protected]> > Reviewed-by: Warner Losh <[email protected]> I looked in bsd-user, to where this was also copied, and couldn't figure out what it was talking about... Though that's a weak review, imho.. > -- > Alex Bennée > >
