Mercurial > hg
view tests/helpers-testrepo.sh @ 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_ & $hg commit -Am _; wait
-abort: No such file or directory: '/tmp/repo/.hg/wlock'
adding a
+warning: ignoring unknown working parent 679a8959a8ca!
+nothing changed
Differential Revision: https://phab.mercurial-scm.org/D7199
author | Valentin Gatien-Baron <valentin.gatienbaron@gmail.com> |
---|---|
date | Mon, 18 Nov 2019 20:10:38 -0800 |
parents | 152f1b47e0ad |
children |
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# In most cases, the mercurial repository can be read by the bundled hg, but # that isn't always true because third-party extensions may change the store # format, for example. In which case, the system hg installation is used. # # We want to use the hg version being tested when interacting with the test # repository, and the system hg when interacting with the mercurial source code # repository. # # The mercurial source repository was typically orignally cloned with the # system mercurial installation, and may require extensions or settings from # the system installation. if [ -n "$HGTESTEXTRAEXTENSIONS" ]; then for extension in $HGTESTEXTRAEXTENSIONS; do extraoptions="$extraoptions --config extensions.$extension=!" done fi syshg () { ( syshgenv exec hg "$@" ) } # Revert the environment so that running "hg" runs the system hg # rather than the test hg installation. syshgenv () { . "$HGTEST_RESTOREENV" HGPLAIN=1 export HGPLAIN } # The test-repo is a live hg repository which may have evolution markers # created, e.g. when a ~/.hgrc enabled evolution. # # Tests may be run using a custom HGRCPATH, which do not enable evolution # markers by default. # # If test-repo includes evolution markers, and we do not enable evolution # markers, hg will occasionally complain when it notices them, which disrupts # tests resulting in sporadic failures. # # Since we aren't performing any write operations on the test-repo, there's # no harm in telling hg that we support evolution markers, which is what the # following lines for the hgrc file do: cat >> "$HGRCPATH" << EOF [experimental] evolution = createmarkers EOF # Use the system hg command if the bundled hg can't read the repository with # no warning nor error. if [ -n "`hg id -R "$TESTDIR/.." 2>&1 >/dev/null`" ]; then alias testrepohg=syshg alias testrepohgenv=syshgenv else alias testrepohg="hg $extraoptions" alias testrepohgenv=: fi