From: Dave Jiang <djiang@mvista•com>
To: linuxppc-dev@ozlabs•org
Subject: Re: mmap on PPC removes file refcount?
Date: Mon, 26 Nov 2007 15:30:59 -0700 [thread overview]
Message-ID: <474B4923.905@mvista.com> (raw)
In-Reply-To: <47435338.2050107@mvista.com>
NM, it was a bad test causing weird behavior on PPC. :(
Dave Jiang wrote:
> It seems the mmap() userland call on PPC causes the kernel to lose the ref
> count for the mount point. This is what I did on a prpmc2800 board (74xx) with
> latest powerpc.git tree (but also seem to happen on 8548 as well).
>
> I mounted an IDE partition. The userland test app opens a file on the mounted
> partition and sits in a sleep loop while holding the file open. I call umount
> on the partition and I get "device is busy" which is suppose to happen.
> However, after the test app calls mmap on the file id for the opened file, I
> can successfully umount even though it should still say "device is busy". This
> does not happen on x86 so I'm assuming something is going on with just PPC.
>
> So using lsof I can list the opened files on a particular partition. When the
> file is opened, it lists 1 entry. When mmaped, on x86 it would list 2 entries,
> but on ppc it lists nothing. Not only did the mmaped entry not show up, the
> entry caused by open disappeared as well. Also, I put a printk in do_umount()
> to see what the refcount is. On x86, it would be 3 and thus causes device busy.
> On PPC it is 3 when the file is openend, however if mmap is called, the
> refcount becomes 2 and thus umount proceeds. It's almost as if the mmap call
> wiped out the opened file entry and decremented the mount count as well.
>
>
--
------------------------------------------------------
Dave Jiang
Software Engineer
MontaVista Software, Inc.
http://www.mvista.com
------------------------------------------------------
next prev parent reply other threads:[~2007-11-26 22:28 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-20 21:35 mmap on PPC removes file refcount? Dave Jiang
2007-11-26 22:30 ` Dave Jiang [this message]
2007-11-26 22:38 ` Benjamin Herrenschmidt
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