Re: [PATCH] Restore previous sigmask in gdb.block_signals

[Tom de Vries <tdevries@suse.de>]

On 7/28/23 20:10, Tom Tromey wrote:
> Tom de Vries found a bug where, sometimes, a SIGCHLD would be
> delivered to a non-main thread, wreaking havoc.
> 
> The problem is that gdb.block_signals was unblocking the signals it
> blocked -- but it was being called from the DAP thread, leading to
> SIGCHLD being unblocked there.
> 
> This patch fixes the problem by restoring the previous set of signals
> instead.
> 

I've done a build and reg-test on x86_64-linux, no regressions.

I also build this in combination with the assert patch mentioned in the 
PR, and ran the dap tests 50 times, and the assert no longer triggers.

Also, the patch LGTM.

I had a bit of trouble parsing the commit message, I'd suggest for 
instance instead:
...
The problem is that gdb.block_signals after first blocking a set of 
signals, then unblocked the same set rather than restoring the initial 
situation.  This function being called from the DAP thread lead to 
SIGCHLD being unblocked there.
...

Tested-by: Tom de Vries <tdevries@suse.de>
Reviewed-By: Tom de Vries <tdevries@suse.de>

Thanks,
- Tom

> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30680
> ---
>   gdb/python/lib/gdb/__init__.py | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
> index 98aadb1dfea..b3124369fe8 100644
> --- a/gdb/python/lib/gdb/__init__.py
> +++ b/gdb/python/lib/gdb/__init__.py
> @@ -271,11 +271,11 @@ def blocked_signals():
>           return
>   
>       to_block = {signal.SIGCHLD, signal.SIGINT, signal.SIGALRM, signal.SIGWINCH}
> -    signal.pthread_sigmask(signal.SIG_BLOCK, to_block)
> +    old_mask = signal.pthread_sigmask(signal.SIG_BLOCK, to_block)
>       try:
>           yield None
>       finally:
> -        signal.pthread_sigmask(signal.SIG_UNBLOCK, to_block)
> +        signal.pthread_sigmask(signal.SIG_SETMASK, old_mask)
>   
>   
>   class Thread(threading.Thread):