Re: [RFC] linux-user: Remove stale "not threadsafe" comments

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> 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 <peter.maydell@linaro.org>
> ---
> 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 <alex.bennee@linaro.org>

-- 
Alex Bennée