Mercurial > hg
view tests/test-changelog-exec.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 | d4e62df1c73d |
children | ccd76e292be5 |
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#require execbit b51a8138292a introduced a regression where we would mention in the changelog executable files added by the second parent of a merge. Test that that doesn't happen anymore $ hg init repo $ cd repo $ echo foo > foo $ hg ci -qAm 'add foo' $ echo bar > bar $ chmod +x bar $ hg ci -qAm 'add bar' manifest of p2: $ hg manifest bar foo $ hg up -qC 0 $ echo >> foo $ hg ci -m 'change foo' created new head manifest of p1: $ hg manifest foo $ hg merge 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ chmod +x foo $ hg ci -m 'merge' this should not mention bar but should mention foo: $ hg tip -v changeset: 3:c53d17ff3380 tag: tip parent: 2:ed1b79f46b9a parent: 1:d394a8db219b user: test date: Thu Jan 01 00:00:00 1970 +0000 files: foo description: merge $ hg debugindex bar rev linkrev nodeid p1 p2 0 1 b004912a8510 000000000000 000000000000 $ cd ..