upstream/mercurial-mirror Files · mercurial/node.py

lock: fix race in lock-breaking code...

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

Augie Fackler - - Load All Authors

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      # node.py - basic nodeid manipulation for mercurial

      #

      # Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>

      #

      # This software may be used and distributed according to the terms of the

      # GNU General Public License version 2 or any later version.

      from __future__ import absolute_import

      import binascii

      # This ugly style has a noticeable effect in manifest parsing

      hex = binascii.hexlify

      # Adapt to Python 3 API changes. If this ends up showing up in

      # profiles, we can use this version only on Python 3, and forward

      # binascii.unhexlify like we used to on Python 2.

      def bin(s):

          try:

              return binascii.unhexlify(s)

          except binascii.Error as e:

              raise TypeError(e)

      nullrev = -1

      # In hex, this is '0000000000000000000000000000000000000000'

      nullid = b"\0" * 20

      nullhex = hex(nullid)

      # Phony node value to stand-in for new files in some uses of

      # manifests.

      # In hex, this is '2121212121212121212121212121212121212121'

      newnodeid = b'!!!!!!!!!!!!!!!!!!!!'

      # In hex, this is '3030303030303030303030303030306164646564'

      addednodeid = b'000000000000000added'

      # In hex, this is '3030303030303030303030306d6f646966696564'

      modifiednodeid = b'000000000000modified'

      wdirfilenodeids = {newnodeid, addednodeid, modifiednodeid}

      # pseudo identifiers for working directory

      # (they are experimental, so don't add too many dependencies on them)

      wdirrev = 0x7FFFFFFF

      # In hex, this is 'ffffffffffffffffffffffffffffffffffffffff'

      wdirid = b"\xff" * 20

      wdirhex = hex(wdirid)

      def short(node):

          return hex(node[:6])

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				# node.py - basic nodeid manipulation for mercurial
				#
				# Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>
				#
				# This software may be used and distributed according to the terms of the
				# GNU General Public License version 2 or any later version.

				from __future__ import absolute_import

				import binascii

				# This ugly style has a noticeable effect in manifest parsing
				hex = binascii.hexlify
				# Adapt to Python 3 API changes. If this ends up showing up in
				# profiles, we can use this version only on Python 3, and forward
				# binascii.unhexlify like we used to on Python 2.
				def bin(s):
				try:
				return binascii.unhexlify(s)
				except binascii.Error as e:
				raise TypeError(e)


				nullrev = -1
				# In hex, this is '0000000000000000000000000000000000000000'
				nullid = b"\0" * 20
				nullhex = hex(nullid)

				# Phony node value to stand-in for new files in some uses of
				# manifests.
				# In hex, this is '2121212121212121212121212121212121212121'
				newnodeid = b'!!!!!!!!!!!!!!!!!!!!'
				# In hex, this is '3030303030303030303030303030306164646564'
				addednodeid = b'000000000000000added'
				# In hex, this is '3030303030303030303030306d6f646966696564'
				modifiednodeid = b'000000000000modified'

				wdirfilenodeids = {newnodeid, addednodeid, modifiednodeid}

				# pseudo identifiers for working directory
				# (they are experimental, so don't add too many dependencies on them)
				wdirrev = 0x7FFFFFFF
				# In hex, this is 'ffffffffffffffffffffffffffffffffffffffff'
				wdirid = b"\xff" * 20
				wdirhex = hex(wdirid)


				def short(node):
				return hex(node[:6])