Mercurial > hg
view tests/test-encode.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 | 538353b80676 |
children | b7fde9237c92 |
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Test encode/decode filters $ hg init $ cat > .hg/hgrc <<EOF > [encode] > not.gz = tr [:lower:] [:upper:] > *.gz = gzip -d > [decode] > not.gz = tr [:upper:] [:lower:] > *.gz = gzip > EOF $ echo "this is a test" | gzip > a.gz $ echo "this is a test" > not.gz $ hg add * $ hg ci -m "test" no changes $ hg status $ touch * no changes $ hg status check contents in repo are encoded $ hg debugdata a.gz 0 this is a test $ hg debugdata not.gz 0 THIS IS A TEST check committed content was decoded $ gunzip < a.gz this is a test $ cat not.gz this is a test $ rm * $ hg co -C 2 files updated, 0 files merged, 0 files removed, 0 files unresolved check decoding of our new working dir copy $ gunzip < a.gz this is a test $ cat not.gz this is a test check hg cat operation $ hg cat a.gz this is a test $ hg cat --decode a.gz | gunzip this is a test $ mkdir subdir $ cd subdir $ hg -R .. cat ../a.gz this is a test $ hg -R .. cat --decode ../a.gz | gunzip this is a test $ cd .. check tempfile filter $ hg cat a.gz --decode --config 'decode.*.gz=tempfile:gzip -c INFILE > OUTFILE' | gunzip this is a test $ hg cat a.gz --decode --config 'decode.*.gz=tempfile:sh -c "exit 1"' abort: command '*' failed: exited with status 1 (glob) [255] $ cd ..