linux: follow up on cpulist parsing (#2973)

`_get_eligible_cpus()` was only parsing a single `N-M` range, so a value
like `0-3,8` would fall back to all CPUs instead of returning the actual
eligible CPU list.

This adds `_parse_cpulist()` returning the expanded CPU IDs and uses it
in `_get_eligible_cpus()`.

For example:

`0-3,8` -> `[0, 1, 2, 3, 8]`

Also added parser coverage and a regression test for the non-contiguous
`Cpus_allowed_list` case.

Tested with:

* `tests/test_linux.py`: 131 passed, 4 skipped
* Ruff
* Black
* `git diff --check`

Author: fabiancrt

psutil/_pslinux.py

@@ -493,6 +493,29 @@ def per_cpu_times():
         return cpus
 
 
+def _parse_cpulist(cpulist):
+    """Parse Linux CPU list string (e.g "0-3,8,10-11")"""
+    cpulist = cpulist.strip()
+    if not cpulist:
+        return []
+    cpus = []
+    for chunk in cpulist.split(','):
+        chunk = chunk.strip()
+        if not chunk:
+            continue
+        if '-' in chunk:
+            start, _, end = chunk.partition('-')
+            start = int(start)
+            end = int(end)
+            if start > end:
+                msg = f"invalid CPU range {chunk!r}"
+                raise ValueError(msg)
+            cpus.extend(range(start, end + 1))
+        else:
+            cpus.append(int(chunk))
+    return cpus
+
+
 def cpu_count_logical():
     """Return the number of logical CPUs in the system."""
     try:
@@ -2117,14 +2140,21 @@ def cpu_affinity_get(self):
             return _psutil.proc_cpu_affinity_get(self.pid)
 
         def _get_eligible_cpus(
-            self, _re=re.compile(br"Cpus_allowed_list:\t(\d+)-(\d+)")
+            self,
+            _re=re.compile(
+                br"^Cpus_allowed_list:[ \t]*([^\r\n]*)", re.MULTILINE
+            ),
         ):
             # See: https://github.com/giampaolo/psutil/issues/956
             data = self._read_status_file()
-            if match := _re.findall(data):
-                return list(range(int(match[0][0]), int(match[0][1]) + 1))
-            else:
-                return list(range(len(per_cpu_times())))
+            if match := _re.search(data):
+                try:
+                    return _parse_cpulist(decode(match.group(1)))
+                except ValueError as err:
+                    debug(
+                        f"can't parse Cpus_allowed_list ({err}); falling back"
+                    )
+            return list(range(len(per_cpu_times())))
 
         @wrap_exceptions
         def cpu_affinity_set(self, cpus):

tests/test_linux.py

@@ -52,6 +52,7 @@
     from psutil._pslinux import CLOCK_TICKS
     from psutil._pslinux import RootFsDeviceFinder
     from psutil._pslinux import _cpu_get_cpuinfo_freq
+    from psutil._pslinux import _parse_cpulist
     from psutil._pslinux import calculate_avail_vmem
     from psutil._pslinux import open_binary
 
@@ -2507,6 +2508,12 @@ def test_status_file_parsing(self):
             assert gids.saved == 1006
             assert p._proc._get_eligible_cpus() == list(range(8))
 
+    def test_status_file_cpus_allowed_list(self):
+        content = b"Cpus_allowed_list:\t0-3,8\n"
+        with mock_open_content({f"/proc/{os.getpid()}/status": content}):
+            p = psutil.Process()
+            assert p._proc._get_eligible_cpus() == [0, 1, 2, 3, 8]
+
     def test_net_connections_enametoolong(self):
         # Simulate a case where /proc/{pid}/fd/{fd} symlink points to
         # a file with full path longer than PATH_MAX, see:
@@ -2620,11 +2627,9 @@ def test_cpu_affinity(self):
     def test_cpu_affinity_eligible_cpus(self):
         value = self.read_status_file("Cpus_allowed_list:")
         with mock.patch("psutil._pslinux.per_cpu_times") as m:
-            self.proc._proc._get_eligible_cpus()
-        if '-' in str(value):
-            assert not m.called
-        else:
-            assert m.called
+            cpus = self.proc._proc._get_eligible_cpus()
+        assert cpus == _parse_cpulist(str(value))
+        assert not m.called
 
 
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