Mercurial > hg
view tests/test-record.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 | db72f9f6580e |
children | 8d72e29ad1e0 |
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Set up a repo $ cat <<EOF >> $HGRCPATH > [ui] > interactive = true > [extensions] > record = > EOF $ hg init a $ cd a Record help $ hg record -h hg record [OPTION]... [FILE]... interactively select changes to commit If a list of files is omitted, all changes reported by 'hg status' will be candidates for recording. See 'hg help dates' for a list of formats valid for -d/--date. If using the text interface (see 'hg help config'), you will be prompted for whether to record changes to each modified file, and for files with multiple changes, for each change to use. For each query, the following responses are possible: y - record this change n - skip this change e - edit this change manually s - skip remaining changes to this file f - record remaining changes to this file d - done, skip remaining changes and files a - record all changes to all remaining files q - quit, recording no changes ? - display help This command is not available when committing a merge. (use 'hg help -e record' to show help for the record extension) options ([+] can be repeated): -A --addremove mark new/missing files as added/removed before committing --close-branch mark a branch head as closed --amend amend the parent of the working directory -s --secret use the secret phase for committing -e --edit invoke editor on commit messages -I --include PATTERN [+] include names matching the given patterns -X --exclude PATTERN [+] exclude names matching the given patterns -m --message TEXT use text as commit message -l --logfile FILE read commit message from file -d --date DATE record the specified date as commit date -u --user USER record the specified user as committer -S --subrepos recurse into subrepositories -w --ignore-all-space ignore white space when comparing lines -b --ignore-space-change ignore changes in the amount of white space -B --ignore-blank-lines ignore changes whose lines are all blank -Z --ignore-space-at-eol ignore changes in whitespace at EOL (some details hidden, use --verbose to show complete help) Select no files $ touch empty-rw $ hg add empty-rw $ hg record empty-rw<<EOF > n > EOF diff --git a/empty-rw b/empty-rw new file mode 100644 abort: empty commit message [255] $ hg tip -p changeset: -1:000000000000 tag: tip user: date: Thu Jan 01 00:00:00 1970 +0000