Mercurial > hg
view tests/test-revset-dirstate-parents.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_ & $hg commit -Am _; wait
-abort: No such file or directory: '/tmp/repo/.hg/wlock'
adding a
+warning: ignoring unknown working parent 679a8959a8ca!
+nothing changed
Differential Revision: https://phab.mercurial-scm.org/D7199
author | Valentin Gatien-Baron <valentin.gatienbaron@gmail.com> |
---|---|
date | Mon, 18 Nov 2019 20:10:38 -0800 |
parents | 7bbc4e113e5f |
children |
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$ HGENCODING=utf-8 $ export HGENCODING $ try() { > hg debugrevspec --debug $@ > } $ log() { > hg log --template '{rev}\n' -r "$1" > } $ hg init repo $ cd repo $ try 'p1()' (func (symbol 'p1') None) * set: <baseset []> $ try 'p2()' (func (symbol 'p2') None) * set: <baseset []> $ try 'parents()' (func (symbol 'parents') None) * set: <baseset+ []> null revision $ log 'p1()' $ log 'p2()' $ log 'parents()' working dir with a single parent $ echo a > a $ hg ci -Aqm0 $ log 'p1()' 0 $ log 'tag() and p1()' $ log 'p2()' $ log 'parents()' 0 $ log 'tag() and parents()' merge in progress $ echo b > b $ hg ci -Aqm1 $ hg up -q 0 $ echo c > c $ hg ci -Aqm2 $ hg merge -q $ log 'p1()' 2 $ log 'p2()' 1 $ log 'tag() and p2()' $ log 'parents()' 1 2 $ cd ..