Note the concurrent seek() trigger in the NEWS and comment

Author: tonghuaroot

Misc/NEWS.d/next/Library/2026-07-11-12-21-12.gh-issue-153539.gBs2T5.rst

@@ -1,2 +1,3 @@
 Fix a crash in the C implementation of :meth:`io.TextIOWrapper.tell` when the
-decoder's ``getstate`` method triggers a reentrant seek. Patch by tonghuaroot.
+decoder's ``getstate`` method triggers a reentrant seek, or when another thread
+seeks the same stream concurrently. Patch by tonghuaroot.

Modules/_io/textio.c

@@ -2875,7 +2875,7 @@ _io_TextIOWrapper_tell_impl(textio *self)
 
     assert (PyBytes_Check(next_input));
 
-    /* Own next_input: a reentrant seek in the decoder can drop self->snapshot. */
+    /* Own next_input: a reentrant or concurrent seek can drop the snapshot. */
     Py_INCREF(next_input);
 
     cookie.start_pos -= PyBytes_GET_SIZE(next_input);