Date: Tue, 11 Oct 2011 00:56:47 -0700 From: Kirk McKusick <mckusick@mckusick.com> To: Garrett Cooper <yanegomi@gmail.com> Cc: Attilio Rao <attilio@freebsd.org>, Xin LI <delphij@freebsd.org>, freebsd-fs@freebsd.org Subject: Re: Need to force sync(2) before umounting UFS1 filesystems? Message-ID: <201110110756.p9B7ul0g051037@chez.mckusick.com> In-Reply-To: <CAGH67wS%2BAW9zYnq=KQzKoVSfM5Oiax%2Bej=tfJ5BvjZHzb6zavA@mail.gmail.com>
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> Date: Mon, 10 Oct 2011 19:12:59 -0700
> From: Garrett Cooper <yanegomi@gmail.com>
> To: Kostik Belousov <kostikbel@gmail.com>
> Cc: Kirk McKusick <mckusick@mckusick.com>, Attilio Rao <attilio@freebsd.org>,
> Xin LI <delphij@freebsd.org>, freebsd-fs@freebsd.org
> Subject: Re: Need to force sync(2) before umounting UFS1 filesystems?
>
> 2011/10/10 Kostik Belousov <kostikbel@gmail.com>:
>
> > The real case to test is the NFS mount which is wedged due to
> > hung/unresponsive NFS server. I have high suspect that the patch
> > could introduce the unkillable hung unmount process.
>
> It blocked, but I could ^C it perfectly fine. I tested it via:
>
> Setup:
> 1. Started up FreeNAS 8.x image; it acquired an IP from my server with
> dhcp-75.local.
>
> Test 1:
> 1. mount -t nfs dhcp-75:/mnt/tank /mnt/nfs/ from my test workstation.
> 2. Paused VM.
> 3. umount /mnt/nfs (the command blocked).
> 4. ^C.
> 5. mount | grep /mnt/nfs showed nothing (it had unmounted).
>
> Test 2:
> 1. mount -t nfs dhcp-75:/mnt/tank /mnt/nfs/ from my test workstation (blocked).
> 2. Opened up another ssh session and cd'ed to /mnt/nfs .
> 3. Paused VM.
> 4. umount /mnt/nfs . It failed with EBUSY.
> 5. mount | grep /mnt/nfs showed that it was still mounted, as expected.
>
> So unless there are buffers still waiting to be written out to an
> NFS share, or other reasons that would prevent the NFS share from
> being fully released, I doubt the proposed behavior is really
> different from previous versions of FreeBSD.
> Thanks,
> -Garrett
Given the testing that has been done and our discussion about deadlocks,
I believe that I should proceed to check in my originally proposed change.
Notably the one that simply deleted the != MNT_FORCE conditional. However,
there is no harm in using my revised version that releases the covered vnode before draining vfs_busy, and there might be some future case where that would be a necessary thing to do.
Speak up if you think I should not proceed to check in this change.
Also, let me know if you have thoughts on which version I should use.
Kirk McKusick
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