blinkseb opened a new pull request, #30243:
URL: https://github.com/apache/airflow/pull/30243

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   Hello,
   
   I've found an issue with the handling of the DAG file last modified time 
which can trigger an infinite parsing loop, when `file_parsing_sort_mode` is 
set to `modified_time` (which seems to be the default value).
   
   `os.path.getmtime()` returns a timestamp, which is converted to a datetime 
using `datetime.fromtimestamp`. According to the documentation:
   
   > If optional argument tz is None or not specified, the timestamp is 
converted to the platform’s local date and time, and the returned 
[datetime](https://docs.python.org/3/library/datetime.html#datetime.datetime) 
object is naive.
   
   The resulting datetime is then made aware using `timezone.make_aware` using 
the user configured timezone, which is not guarantee to be the same as the 
platform's timezone. If that's not the case, we can end up with modified time 
in the future and trigger an infinite parsing loop.
   
   The fix is to use `datetime.utcfromtimestamp` to convert the timestamp, to 
force the resulting datetime in UTC, and explicitly specify the UTC timezone to 
`make_aware`.
   
   ---
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