Mercurial > hg
view tests/test-remotefilelog-bundle2-legacy.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 | 0800d9e6e216 |
children | 68b7faeb6ef3 |
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#require no-windows $ . "$TESTDIR/remotefilelog-library.sh" generaldelta to generaldelta interactions with bundle2 but legacy clients without changegroup2 support $ cat > testcg2.py << EOF > import sys > from mercurial import changegroup, registrar, util > cmdtable = {} > command = registrar.command(cmdtable) > @command('testcg2', norepo=True) > def testcg2(ui): > if not util.safehasattr(changegroup, 'cg2packer'): > sys.exit(80) > EOF $ cat >> $HGRCPATH << EOF > [extensions] > testcg2 = $TESTTMP/testcg2.py > EOF $ hg testcg2 || exit 80 $ cat > disablecg2.py << EOF > from mercurial import changegroup, error, util > deleted = False > def reposetup(ui, repo): > global deleted > if deleted: > return > packermap = changegroup._packermap > # protect against future changes > if len(packermap) != 3: > raise error.Abort('packermap has %d versions, expected 3!' % len(packermap)) > for k in ['01', '02', '03']: > if not packermap.get(k): > raise error.Abort("packermap doesn't have key '%s'!" % k) > > del packermap['02'] > deleted = True > EOF $ hg init master $ grep generaldelta master/.hg/requires generaldelta $ cd master preferuncompressed = False so that we can make both generaldelta and non-generaldelta clones $ cat >> .hg/hgrc <<EOF > [remotefilelog] > server=True > [experimental] > bundle2-exp = True > [server] > preferuncompressed = False > EOF $ echo x > x $ hg commit -qAm x $ cd .. $ hgcloneshallow ssh://user@dummy/master shallow -q --pull --config experimental.bundle2-exp=True 1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob) $ cd shallow $ cat >> .hg/hgrc << EOF > [extensions] > disablecg2 = $TESTTMP/disablecg2.py > EOF $ cd ../master $ echo y > y $ hg commit -qAm y $ cd ../shallow $ hg pull -u pulling from ssh://user@dummy/master searching for changes adding changesets adding manifests adding file changes added 1 changesets with 0 changes to 0 files new changesets d34c38483be9 1 files updated, 0 files merged, 0 files removed, 0 files unresolved 1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob) $ echo a > a $ hg commit -qAm a $ hg push pushing to ssh://user@dummy/master searching for changes remote: adding changesets remote: adding manifests remote: adding file changes remote: added 1 changesets with 1 changes to 1 files