Mercurial > hg
view tests/test-check-help.t @ 43709:039fbd14d4e2
lock: fix race in lock-breaking code
With low frequency, I see hg pulls fail with output like:
abort: no such file or directory: .hg/store/lock
I think what happens is, in lock.py, in:
def _testlock(self, locker):
if not self._lockshouldbebroken(locker):
return locker
# if locker dead, break lock. must do this with another lock
# held, or can race and break valid lock.
try:
with lock(self.vfs, self.f + b'.break', timeout=0):
self.vfs.unlink(self.f)
except error.LockError:
return locker
if a lock is breakable on disk, and two hg processes concurrently get
to the "if locker dead" comment, a possible interleaving is: process1
finishes executing the function and then process2 finishes executing
the function. If that happens, process2 will either get ENOENT in
self.vfs.unlink (resulting in the spurious failure above), or break a
valid lock and potentially cause repository corruption.
The fix is simple enough: make sure the lock is breakable _inside_ the
critical section, because only then can we know that no other process
can invalidate our knowledge on the lock on disk.
I don't think there are tests for this. I've tested this manually
with:
diff --git a/mercurial/lock.py b/mercurial/lock.py
--- a/mercurial/lock.py
+++ b/mercurial/lock.py
@@ -351,6 +351,8 @@ class lock(object):
if not self._lockshouldbebroken(locker):
return locker
+ import random
+ time.sleep(1. + random.random())
# if locker dead, break lock. must do this with another lock
# held, or can race and break valid lock.
try:
@@ -358,6 +360,7 @@ class lock(object):
self.vfs.unlink(self.f)
except error.LockError:
return locker
+ time.sleep(1)
def testlock(self):
"""return id of locker if lock is valid, else None.
and I see this change of behavior before/after this commit:
$ $hg init repo
$ cd repo
$ ln -s $HOSTNAME/effffffc:987654321 .hg/wlock
$ touch a
$ $hg commit -Am_ & $hg commit -Am _; wait
-abort: No such file or directory: '/tmp/repo/.hg/wlock'
adding a
+warning: ignoring unknown working parent 679a8959a8ca!
+nothing changed
Differential Revision: https://phab.mercurial-scm.org/D7199
author | Valentin Gatien-Baron <valentin.gatienbaron@gmail.com> |
---|---|
date | Mon, 18 Nov 2019 20:10:38 -0800 |
parents | b6c610bf567e |
children | 42d2b31cee0b |
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#require test-repo $ . "$TESTDIR/helpers-testrepo.sh" $ cat <<'EOF' > scanhelptopics.py > from __future__ import absolute_import, print_function > import re > import sys > if sys.platform == "win32": > import msvcrt > import os > msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY) > stdout = getattr(sys.stdout, 'buffer', sys.stdout) > topics = set() > topicre = re.compile(br':hg:`help ([a-z0-9\-.]+)`') > for fname in sys.argv: > with open(fname, 'rb') as f: > topics.update(m.group(1) for m in topicre.finditer(f.read())) > for s in sorted(topics): > stdout.write(b'%s\n' % s) > EOF $ cd "$TESTDIR"/.. Check if ":hg:`help TOPIC`" is valid: (use "xargs -n1 -t" to see which help commands are executed) $ testrepohg files 'glob:{hgdemandimport,hgext,mercurial}/**/*.py' \ > | sed 's|\\|/|g' \ > | xargs "$PYTHON" "$TESTTMP/scanhelptopics.py" \ > | xargs -n1 hg help --config extensions.phabricator= > /dev/null