Mercurial > hg
view tests/test-histedit-bookmark-motion.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_ & $hg commit -Am _; wait
-abort: No such file or directory: '/tmp/repo/.hg/wlock'
adding a
+warning: ignoring unknown working parent 679a8959a8ca!
+nothing changed
Differential Revision: https://phab.mercurial-scm.org/D7199
author | Valentin Gatien-Baron <valentin.gatienbaron@gmail.com> |
---|---|
date | Mon, 18 Nov 2019 20:10:38 -0800 |
parents | 4441705b7111 |
children | 6f8a94bbfba1 |
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$ . "$TESTDIR/histedit-helpers.sh" $ cat >> $HGRCPATH <<EOF > [extensions] > histedit= > EOF $ hg init r $ cd r $ for x in a b c d e f ; do > echo $x > $x > hg add $x > hg ci -m $x > done $ hg book -r 1 will-move-backwards $ hg book -r 2 two $ hg book -r 2 also-two $ hg book -r 3 three $ hg book -r 4 four $ hg book -r tip five $ hg log --graph @ changeset: 5:652413bf663e | bookmark: five | tag: tip | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: f | o changeset: 4:e860deea161a | bookmark: four | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: e | o changeset: 3:055a42cdd887 | bookmark: three | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: d | o changeset: 2:177f92b77385 | bookmark: also-two | bookmark: two | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: c | o changeset: 1:d2ae7f538514 | bookmark: will-move-backwards | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: b | o changeset: 0:cb9a9f314b8b user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: a $ HGEDITOR=cat hg histedit 1 pick d2ae7f538514 1 b pick 177f92b77385 2 c pick 055a42cdd887 3 d pick e860deea161a 4 e pick 652413bf663e 5 f # Edit history between d2ae7f538514 and 652413bf663e # # Commits are listed from least to most recent # # You can reorder changesets by reordering the lines # # Commands: # # e, edit = use commit, but stop for amending # m, mess = edit commit message without changing commit content # p, pick = use commit # b, base = checkout changeset and apply further changesets from there # d, drop = remove commit from history # f, fold = use commit, but combine it with the one above # r, roll = like fold, but discard this commit's description and date # $ hg histedit 1 --commands - --verbose << EOF | grep histedit > pick 177f92b77385 2 c > drop d2ae7f538514 1 b > pick 055a42cdd887 3 d > fold e860deea161a 4 e > pick 652413bf663e 5 f > EOF saved backup bundle to $TESTTMP/r/.hg/strip-backup/96e494a2d553-45c027ab-histedit.hg $ hg log --graph @ changeset: 3:cacdfd884a93 | bookmark: five | tag: tip | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: f | o changeset: 2:59d9f330561f | bookmark: four | bookmark: three | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: d | o changeset: 1:b346ab9a313d | bookmark: also-two | bookmark: two | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: c | o changeset: 0:cb9a9f314b8b bookmark: will-move-backwards user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: a $ HGEDITOR=cat hg histedit 1 pick b346ab9a313d 1 c pick 59d9f330561f 2 d pick cacdfd884a93 3 f # Edit history between b346ab9a313d and cacdfd884a93 # # Commits are listed from least to most recent # # You can reorder changesets by reordering the lines # # Commands: # # e, edit = use commit, but stop for amending # m, mess = edit commit message without changing commit content # p, pick = use commit # b, base = checkout changeset and apply further changesets from there # d, drop = remove commit from history # f, fold = use commit, but combine it with the one above # r, roll = like fold, but discard this commit's description and date # $ hg histedit 1 --commands - --verbose << EOF | grep histedit > pick b346ab9a313d 1 c > pick cacdfd884a93 3 f > pick 59d9f330561f 2 d > EOF saved backup bundle to $TESTTMP/r/.hg/strip-backup/59d9f330561f-073008af-histedit.hg We expect 'five' to stay at tip, since the tipmost bookmark is most likely the useful signal. $ hg log --graph @ changeset: 3:c04e50810e4b | bookmark: five | bookmark: four | bookmark: three | tag: tip | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: d | o changeset: 2:c13eb81022ca | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: f | o changeset: 1:b346ab9a313d | bookmark: also-two | bookmark: two | user: test | date: Thu Jan 01 00:00:00 1970 +0000 | summary: c | o changeset: 0:cb9a9f314b8b bookmark: will-move-backwards user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: a