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())

1. if locker dead, break lock. must do this with another lock
2. 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