Mercurial > hg
view tests/test-ui-verbosity.py.out @ 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 | 807f3f5c60e9 |
children |
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hgrc settings command line options final result quiet verbo debug quiet verbo debug quiet verbo debug 0 False False False False False False -> False False False 1 True False False False False False -> True False False 2 False True False False False False -> False True False 3 True True False False False False -> False False False 4 False False True False False False -> False True True 5 True False True False False False -> False True True 6 False True True False False False -> False True True 7 True True True False False False -> False True True 8 False False False True False False -> True False False 9 True False False True False False -> True False False 10 False True False True False False -> True False False 11 True True False True False False -> True False False 12 False False True True False False -> True False False 13 True False True True False False -> True False False 14 False True True True False False -> True False False 15 True True True True False False -> True False False 16 False False False False True False -> False True False 17 True False False False True False -> False True False 18 False True False False True False -> False True False 19 True True False False True False -> False True False 20 False False True False True False -> False True False 21 True False True False True False -> False True False 22 False True True False True False -> False True False 23 True True True False True False -> False True False 24 False False False True True False -> False False False 25 True False False True True False -> False False False 26 False True False True True False -> False False False 27 True True False True True False -> False False False 28 False False True True True False -> False False False 29 True False True True True False -> False False False 30 False True True True True False -> False False False 31 True True True True True False -> False False False 32 False False False False False True -> False True True 33 True False False False False True -> False True True 34 False True False False False True -> False True True 35 True True False False False True -> False True True 36 False False True False False True -> False True True 37 True False True False False True -> False True True 38 False True True False False True -> False True True 39 True True True False False True -> False True True 40 False False False True False True -> False True True 41 True False False True False True -> False True True 42 False True False True False True -> False True True 43 True True False True False True -> False True True 44 False False True True False True -> False True True 45 True False True True False True -> False True True 46 False True True True False True -> False True True 47 True True True True False True -> False True True 48 False False False False True True -> False True True 49 True False False False True True -> False True True 50 False True False False True True -> False True True 51 True True False False True True -> False True True 52 False False True False True True -> False True True 53 True False True False True True -> False True True 54 False True True False True True -> False True True 55 True True True False True True -> False True True 56 False False False True True True -> False True True 57 True False False True True True -> False True True 58 False True False True True True -> False True True 59 True True False True True True -> False True True 60 False False True True True True -> False True True 61 True False True True True True -> False True True 62 False True True True True True -> False True True 63 True True True True True True -> False True True