changeset 48438:322525db4c98

status: use filesystem time boundary to invalidate racy mtime

We record the filesystem time at the start of the status walk and use that as a
boundary to detect files that might be modified during (or right after) the
status run without the mtime allowing that edition to be detected.  We
currently do this at a second precision. In a later patch, we will use
nanosecond precision when available.

To cope with "broken" time on the file system where file could be in the
future, we also keep mtime for file over one day in the future. See inline
comment for details.

Large file tests get a bit more confused as we reduce the odds for race
condition.

As a "side effect", the win32text extension is happy again.

Differential Revision: https://phab.mercurial-scm.org/D11794

--- a/hgext/largefiles/lfutil.py	Thu Nov 18 15:00:13 2021 +0100
+++ b/hgext/largefiles/lfutil.py	Thu Nov 18 13:12:40 2021 +0100
@@ -244,7 +244,7 @@
 def lfdirstatestatus(lfdirstate, repo):
     pctx = repo[b'.']
     match = matchmod.always()
-    unsure, s = lfdirstate.status(
+    unsure, s, mtime_boundary = lfdirstate.status(
         match, subrepos=[], ignored=False, clean=False, unknown=False
     )
     modified, clean = s.modified, s.clean
@@ -263,6 +263,10 @@
             size = st.st_size
             mtime = timestamp.mtime_of(st)
             cache_data = (mode, size, mtime)
+            # We should consider using the mtime_boundary
+            # logic here, but largefile never actually had
+            # ambiguity protection before, so this confuse
+            # the tests and need more thinking.
             lfdirstate.set_clean(lfile, cache_data)
     return s
 
@@ -670,7 +674,7 @@
         # large.
         lfdirstate = openlfdirstate(ui, repo)
         dirtymatch = matchmod.always()
-        unsure, s = lfdirstate.status(
+        unsure, s, mtime_boundary = lfdirstate.status(
             dirtymatch, subrepos=[], ignored=False, clean=False, unknown=False
         )
         modifiedfiles = unsure + s.modified + s.added + s.removed

--- a/hgext/largefiles/overrides.py	Thu Nov 18 15:00:13 2021 +0100
+++ b/hgext/largefiles/overrides.py	Thu Nov 18 13:12:40 2021 +0100
@@ -1519,7 +1519,7 @@
         return orig(repo, matcher, prefix, uipathfn, opts)
     # Get the list of missing largefiles so we can remove them
     lfdirstate = lfutil.openlfdirstate(repo.ui, repo)
-    unsure, s = lfdirstate.status(
+    unsure, s, mtime_boundary = lfdirstate.status(
         matchmod.always(),
         subrepos=[],
         ignored=False,
@@ -1746,7 +1746,7 @@
         # (*1) deprecated, but used internally (e.g: "rebase --collapse")
 
         lfdirstate = lfutil.openlfdirstate(repo.ui, repo)
-        unsure, s = lfdirstate.status(
+        unsure, s, mtime_boundary = lfdirstate.status(
             matchmod.always(),
             subrepos=[],
             ignored=False,

--- a/hgext/largefiles/reposetup.py	Thu Nov 18 15:00:13 2021 +0100
+++ b/hgext/largefiles/reposetup.py	Thu Nov 18 13:12:40 2021 +0100
@@ -197,7 +197,7 @@
                     match._files = [f for f in match._files if sfindirstate(f)]
                     # Don't waste time getting the ignored and unknown
                     # files from lfdirstate
-                    unsure, s = lfdirstate.status(
+                    unsure, s, mtime_boundary = lfdirstate.status(
                         match,
                         subrepos=[],
                         ignored=False,
@@ -230,6 +230,10 @@
                                 size = s.st_size
                                 mtime = timestamp.mtime_of(s)
                                 cache_data = (mode, size, mtime)
+                                # We should consider using the mtime_boundary
+                                # logic here, but largefile never actually had
+                                # ambiguity protection before, so this confuse
+                                # the tests and need more thinking.
                                 lfdirstate.set_clean(lfile, cache_data)
                     else:
                         tocheck = unsure + modified + added + clean

--- a/hgext/remotefilelog/__init__.py	Thu Nov 18 15:00:13 2021 +0100
+++ b/hgext/remotefilelog/__init__.py	Thu Nov 18 13:12:40 2021 +0100
@@ -520,7 +520,7 @@
 
 
 # Prefetch files before status attempts to look at their size and contents
-def checklookup(orig, self, files):
+def checklookup(orig, self, files, mtime_boundary):
     repo = self._repo
     if isenabled(repo):
         prefetchfiles = []
@@ -530,7 +530,7 @@
                     prefetchfiles.append((f, hex(parent.filenode(f))))
         # batch fetch the needed files from the server
         repo.fileservice.prefetch(prefetchfiles)
-    return orig(self, files)
+    return orig(self, files, mtime_boundary)
 
 
 # Prefetch the logic that compares added and removed files for renames

--- a/mercurial/context.py	Thu Nov 18 15:00:13 2021 +0100
+++ b/mercurial/context.py	Thu Nov 18 13:12:40 2021 +0100
@@ -1796,13 +1796,14 @@
             sane.append(f)
         return sane
 
-    def _checklookup(self, files):
+    def _checklookup(self, files, mtime_boundary):
         # check for any possibly clean files
         if not files:
-            return [], [], []
+            return [], [], [], []
 
         modified = []
         deleted = []
+        clean = []
         fixup = []
         pctx = self._parents[0]
         # do a full compare of any files that might have changed
@@ -1816,22 +1817,35 @@
                     or pctx[f].cmp(self[f])
                 ):
                     modified.append(f)
+                elif mtime_boundary is None:
+                    clean.append(f)
                 else:
-                    # XXX note that we have a race windows here since we gather
-                    # the stats after we compared so the file might have
-                    # changed.
-                    #
-                    # However this have always been the case and the
-                    # refactoring moving the code here is improving the
-                    # situation by narrowing the race and moving the two steps
-                    # (comparison + stat) in the same location.
-                    #
-                    # Making this code "correct" is now possible.
                     s = self[f].lstat()
                     mode = s.st_mode
                     size = s.st_size
-                    mtime = timestamp.mtime_of(s)
-                    fixup.append((f, (mode, size, mtime)))
+                    file_mtime = timestamp.mtime_of(s)
+                    cache_info = (mode, size, file_mtime)
+
+                    file_second = file_mtime[0]
+                    boundary_second = mtime_boundary[0]
+                    # If the mtime of the ambiguous file is younger (or equal)
+                    # to the starting point of the `status` walk, we cannot
+                    # garantee that another, racy, write will not happen right
+                    # after with the same mtime and we cannot cache the
+                    # information.
+                    #
+                    # However is the mtime is far away in the future, this is
+                    # likely some mismatch between the current clock and
+                    # previous file system operation. So mtime more than one days
+                    # in the future are considered fine.
+                    if (
+                        boundary_second
+                        <= file_second
+                        < (3600 * 24 + boundary_second)
+                    ):
+                        clean.append(f)
+                    else:
+                        fixup.append((f, cache_info))
             except (IOError, OSError):
                 # A file become inaccessible in between? Mark it as deleted,
                 # matching dirstate behavior (issue5584).
@@ -1841,7 +1855,7 @@
                 # it's in the dirstate.
                 deleted.append(f)
 
-        return modified, deleted, fixup
+        return modified, deleted, clean, fixup
 
     def _poststatusfixup(self, status, fixup):
         """update dirstate for files that are actually clean"""
@@ -1895,17 +1909,21 @@
         subrepos = []
         if b'.hgsub' in self:
             subrepos = sorted(self.substate)
-        cmp, s = self._repo.dirstate.status(
+        cmp, s, mtime_boundary = self._repo.dirstate.status(
             match, subrepos, ignored=ignored, clean=clean, unknown=unknown
         )
 
         # check for any possibly clean files
         fixup = []
         if cmp:
-            modified2, deleted2, fixup = self._checklookup(cmp)
+            modified2, deleted2, clean_set, fixup = self._checklookup(
+                cmp, mtime_boundary
+            )
             s.modified.extend(modified2)
             s.deleted.extend(deleted2)
 
+            if clean_set and clean:
+                s.clean.extend(clean_set)
             if fixup and clean:
                 s.clean.extend((f for f, _ in fixup))
 

--- a/mercurial/dirstate.py	Thu Nov 18 15:00:13 2021 +0100
+++ b/mercurial/dirstate.py	Thu Nov 18 13:12:40 2021 +0100
@@ -1308,11 +1308,20 @@
             # Some matchers have yet to be implemented
             use_rust = False
 
+        # Get the time from the filesystem so we can disambiguate files that
+        # appear modified in the present or future.
+        try:
+            mtime_boundary = timestamp.get_fs_now(self._opener)
+        except OSError:
+            # In largefiles or readonly context
+            mtime_boundary = None
+
         if use_rust:
             try:
-                return self._rust_status(
+                res = self._rust_status(
                     match, listclean, listignored, listunknown
                 )
+                return res + (mtime_boundary,)
             except rustmod.FallbackError:
                 pass
 
@@ -1402,7 +1411,7 @@
         status = scmutil.status(
             modified, added, removed, deleted, unknown, ignored, clean
         )
-        return (lookup, status)
+        return (lookup, status, mtime_boundary)
 
     def matches(self, match):
         """

--- a/mercurial/narrowspec.py	Thu Nov 18 15:00:13 2021 +0100
+++ b/mercurial/narrowspec.py	Thu Nov 18 13:12:40 2021 +0100
@@ -323,7 +323,7 @@
     removedmatch = matchmod.differencematcher(oldmatch, newmatch)
 
     ds = repo.dirstate
-    lookup, status = ds.status(
+    lookup, status, _mtime_boundary = ds.status(
         removedmatch, subrepos=[], ignored=True, clean=True, unknown=True
     )
     trackeddirty = status.modified + status.added

--- a/tests/test-dirstate-race.t	Thu Nov 18 15:00:13 2021 +0100
+++ b/tests/test-dirstate-race.t	Thu Nov 18 13:12:40 2021 +0100
@@ -66,11 +66,11 @@
   > )
   > def extsetup(ui):
   >     extensions.wrapfunction(context.workingctx, '_checklookup', overridechecklookup)
-  > def overridechecklookup(orig, self, files):
+  > def overridechecklookup(orig, self, *args, **kwargs):
   >     # make an update that changes the dirstate from underneath
   >     self._repo.ui.system(br"sh '$TESTTMP/dirstaterace.sh'",
   >                          cwd=self._repo.root)
-  >     return orig(self, files)
+  >     return orig(self, *args, **kwargs)
   > EOF
 
   $ hg debugrebuilddirstate