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[3.14] gh-150191: Avoid data race in test_sni_callback_race (GH-150193) #153270

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Merged
kumaraditya303 merged 1 commit into from
Jul 8, 2026
Merged

[3.14] gh-150191: Avoid data race in test_sni_callback_race (GH-150193) #153270

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gh-150191: Avoid data race in test_sni_callback_race (GH-150193) 
(cherry picked from commit fd9d8c3)

Co-authored-by: Sam Gross <colesbury@gmail.com>
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@colesbury @miss-islington
colesbury authored and miss-islington committed Jul 7, 2026
commit 270490b53535e2ef970cbaaf8ffcc28b3df9077a
27 changes: 12 additions & 15 deletions Lib/test/test_ssl.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1533,19 +1533,24 @@ def dummycallback(sock, servername, ctx, cycle=ctx):
gc.collect()
self.assertIs(wr(), None)

@unittest.skipUnless(support.Py_GIL_DISABLED,
"test is only useful if the GIL is disabled")
@threading_helper.requires_working_threading()
def test_sni_callback_race(self):
# Replacing sni_callback while handshakes are in-flight must not
# Replacing sni_callback while a handshake is in-flight must not
# crash (use-after-free on the callback in free-threaded builds).
#
# Use a single handshake thread: OpenSSL has internal data races
# on shared SSL_CTX state when multiple handshakes run
# concurrently against the same context (gh-150191). Concurrency
# on the *setter* is what exercises the fix from gh-149816, so
# multiple toggler threads race against each other and against
# the one handshake worker.
client_ctx, server_ctx, hostname = testing_context()

server_ctx.sni_callback = lambda *a: None
done = threading.Event()
deadline = time.monotonic() + 0.1

def do_handshakes():
while not done.is_set():
while time.monotonic() < deadline:
c_in = ssl.MemoryBIO()
c_out = ssl.MemoryBIO()
s_in = ssl.MemoryBIO()
Expand All @@ -1572,19 +1577,11 @@ def do_handshakes():
c_in.write(s_out.read())

def toggle_callback():
while not done.is_set():
while time.monotonic() < deadline:
server_ctx.sni_callback = lambda *a: None
server_ctx.sni_callback = None

workers = max(4, (os.cpu_count() or 4) * 2)
threads = [threading.Thread(target=do_handshakes)
for _ in range(workers)]
threads.append(threading.Thread(target=toggle_callback))

with threading_helper.catch_threading_exception() as cm:
with threading_helper.start_threads(threads):
done.set()
self.assertIsNone(cm.exc_value)
threading_helper.run_concurrently([do_handshakes] + 4 * [toggle_callback])

def test_cert_store_stats(self):
ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
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