Re-acquire GIL earlier in gdbpy_parse_and_eval
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Commit Message
Tom de Vries filed a bug about an intermittent gdb DAP failure -- and
coincidentally, at the same time, Alexandra Hájková sent email about a
somewhat similar failure.
After looking into this for a while (with no results) using ASan and
valgrind, I found that setting PYTHONMALLOC=malloc_debug found the bug
instantly.
The problem is that gdbpy_parse_and_eval releases the GIL while
calling parse_and_eval, but fails to re-acquire it before calling
value_to_value_object. This is easily fixed by introducing a new
scope.
I wonder whether the test suite should unconditionally set
PYTHONMALLOC=malloc_debug.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30686
---
gdb/python/python.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
Comments
On 7/27/23 15:58, Tom Tromey wrote:
> Tom de Vries filed a bug about an intermittent gdb DAP failure -- and
> coincidentally, at the same time, Alexandra Hájková sent email about a
> somewhat similar failure.
>
> After looking into this for a while (with no results) using ASan and
> valgrind, I found that setting PYTHONMALLOC=malloc_debug found the bug
> instantly.
>
> The problem is that gdbpy_parse_and_eval releases the GIL while
> calling parse_and_eval, but fails to re-acquire it before calling
> value_to_value_object. This is easily fixed by introducing a new
> scope.
>
Hi,
thanks for taking care of this.
I've tested this, and the PR no longer triggers for me.
[ FYI, I also tested for PR30680, both using the assert patch and tsan,
and that one still triggers. ]
Also, patch LGTM.
Tested-by: Tom de Vries <tdevries@suse.de>
Reviewed-By: Tom de Vries <tdevries@suse.de>
Thanks,
- Tom
> I wonder whether the test suite should unconditionally set
> PYTHONMALLOC=malloc_debug.
>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30686
> ---
> gdb/python/python.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/python/python.c b/gdb/python/python.c
> index 505fc4412d1..6a978d632e9 100644
> --- a/gdb/python/python.c
> +++ b/gdb/python/python.c
> @@ -994,9 +994,17 @@ gdbpy_parse_and_eval (PyObject *self, PyObject *args, PyObject *kw)
> PyObject *result = nullptr;
> try
> {
> - gdbpy_allow_threads allow_threads;
> scoped_value_mark free_values;
> - struct value *val = parse_and_eval (expr_str, flags);
> + struct value *val;
> + {
> + /* Allow other Python threads to run while we're evaluating
> + the expression. This is important because the expression
> + could involve inferior calls or otherwise be a lengthy
> + calculation. We take care here to re-acquire the GIL here
> + before continuing with Python work. */
> + gdbpy_allow_threads allow_threads;
> + val = parse_and_eval (expr_str, flags);
> + }
> result = value_to_value_object (val);
> }
> catch (const gdb_exception &except)
Tom> Also, patch LGTM.
Tom> Tested-by: Tom de Vries <tdevries@suse.de>
Tom> Reviewed-By: Tom de Vries <tdevries@suse.de>
Thanks, I'm checking it in.
Tom
@@ -994,9 +994,17 @@ gdbpy_parse_and_eval (PyObject *self, PyObject *args, PyObject *kw)
PyObject *result = nullptr;
try
{
- gdbpy_allow_threads allow_threads;
scoped_value_mark free_values;
- struct value *val = parse_and_eval (expr_str, flags);
+ struct value *val;
+ {
+ /* Allow other Python threads to run while we're evaluating
+ the expression. This is important because the expression
+ could involve inferior calls or otherwise be a lengthy
+ calculation. We take care here to re-acquire the GIL here
+ before continuing with Python work. */
+ gdbpy_allow_threads allow_threads;
+ val = parse_and_eval (expr_str, flags);
+ }
result = value_to_value_object (val);
}
catch (const gdb_exception &except)