From: Ian Kent <raven@themaw.net>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
autofs mailing list <autofs@vger.kernel.org>,
Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Omar Sandoval <osandov@osandov.com>
Subject: Re: [PATCH 1/8] vfs - change d_manage() to take a struct path
Date: Tue, 01 Nov 2016 10:02:03 +0800 [thread overview]
Message-ID: <1477965723.2798.13.camel@themaw.net> (raw)
In-Reply-To: <1477551028.2898.25.camel@themaw.net>
On Thu, 2016-10-27 at 14:50 +0800, Ian Kent wrote:
> On Thu, 2016-10-27 at 10:47 +0800, Ian Kent wrote:
> >
> > On Thu, 2016-10-27 at 03:11 +0100, Al Viro wrote:
> > >
> > >
> > >
> > > How much testing did it get? I've several test setups involving
> > > autofs, but they are nowhere near exhaustive and I don't have good
> > > enough feel of the codebase to slap together something with decent
> > > coverage...
> > It got my standard testing.
> >
> > For that I use a modified version of the autofs Connectathon system.
> >
> > It's more about testing a wide variety of syntax and map setups and so
> > exercises
> > a large number of different types of autofs mounts.
> >
> > It's meant to check normal operation but not so much stress testing even
> > though
> > it does perform quite a few mounts (around 250-300, not to mention the
> > autofs
> > mounts themselves).
> >
> > I have another standard test I call the submount-test and it was originally
> > done
> > to stress test the most common problem I see, concurrent expire to mount.
> >
> > I didn't see any problems I couldn't explain in these but I might need to
> > re-
> > visit the submount-test to see if it is still doing what I want.
> >
> > OTOH, the pattern of mount and umount I see when the submount-test is run
> > does
> > look like it is doing what I want but it might not be getting all the way to
> > the
> > top of the tree of mounts enough times over the course of the test.
> >
> > So I'm happy with my testing, just not as happy as I could be.
> Well, almost happy with my testing.
>
> Naturally I also tested the specific case this series is meant to fix.
>
> Basically:
> ls /mnt/foo # do the initial automount
> unshare -m sleep 10 & # hold the automount in a new namespace
> umount /mnt/foo # pretend the mount timed out
> ls /mnt/foo # try to access it again
> ls: cannot open directory '/mnt/foo': Too many levels of symbolic links
>
> as seen on the autofs mailing list. My specific test was a little different
> but
> verified this was resolved.
>
> Now that Al seems reasonably OK with the series, with some changes, I'll test
> some other use cases, mainly to verify the expire still functions as required.
> That might need more work.
I have done some further tests, specifically for (what I believe are) the two
most common use cases.
First, using automount(8) entirely within a container, as expected works fine.
But the second case, one where automount(8) is run in the root namespace and has
automount directories bound into a container does have a problem.
The problem is due to may_umount_tree() only considering mounts in the root
namespace and leads to expire attempts on mounts even if they are in use in
another namespace.
It's not a serious problem as the umount attempt fails because the mount is busy
but it would be good to avoid the call back overhead.
Unfortunately it looks like transforming may_umount_tree() to use a similar
check to may_umount() introduces a race (picked up by my submount-test) which
I'm struggling to understand, I'll continue to work on it.
Ian
prev parent reply other threads:[~2016-11-01 2:02 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-11 5:33 [PATCH 1/8] vfs - change d_manage() to take a struct path Ian Kent
2016-10-11 5:33 ` [PATCH 2/8] vfs - add path_is_mountpoint() helper Ian Kent
2016-10-11 5:34 ` [PATCH 3/8] vfs - add path_has_submounts() Ian Kent
2016-10-11 5:34 ` [PATCH 4/8] autofs - change autofs4_expire_wait() to take struct path Ian Kent
2016-10-11 5:34 ` [PATCH 5/8] autofs - change autofs4_wait() " Ian Kent
2016-10-11 5:34 ` [PATCH 6/8] autofs - use path_is_mountpoint() to fix unreliable d_mountpoint() checks Ian Kent
2016-10-27 2:17 ` Al Viro
2016-10-27 2:51 ` Ian Kent
2016-10-11 5:34 ` [PATCH 7/8] autofs - use path_has_submounts() to fix unreliable have_submount() checks Ian Kent
2016-10-11 5:34 ` [PATCH 8/8] vfs - remove unused have_submounts() function Ian Kent
2016-10-11 16:04 ` [PATCH 1/8] vfs - change d_manage() to take a struct path Eric W. Biederman
2016-10-11 23:47 ` Ian Kent
2016-10-19 19:40 ` Andrew Morton
2016-10-20 23:39 ` Ian Kent
2016-10-27 2:11 ` Al Viro
2016-10-27 2:47 ` Ian Kent
2016-10-27 6:50 ` Ian Kent
2016-11-01 2:02 ` Ian Kent [this message]
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