Restore previous sigmask in gdb.block_signals
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Commit Message
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.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30680
---
gdb/python/lib/gdb/__init__.py | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
Comments
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):
On 7/29/23 08:25, Tom de Vries via Gdb-patches wrote:
> 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, I build with -fsanitize=thread and tested the dap tests, that's
also clean now.
Thanks,
- Tom
> 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):
>
@@ -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):