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Re: kern/48135: Bad locking for umount
The following reply was made to PR kern/48135; it has been noted by GNATS.
From: "J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>
Subject: Re: kern/48135: Bad locking for umount
Date: Thu, 22 Aug 2013 12:36:21 +0200
On Aug 21, 2013, at 11:20 PM, Michael van Elst <mlelstv%serpens.de@localhost> =
> On Wed, Aug 21, 2013 at 10:35:00AM +0000, J. Hannken-Illjes wrote:
>> This fix looks wrong.
>> If it is possible for the (last) reference to go away while =
>> running it is also unsafe to increment the reference counter here as =
>> could be zero and be freed from vfs_destroy().
> It is supposed to be a precondition to vfs_busy() that the reference =
> is not zero, otherwise it couldn't use the mp pointer for anything.
If this precondition "The caller must hold a pre-existing reference to =
would be met this error could not happen as vfs_busy() will not =
the reference count.
And if this precondition is not met even incrementing the reference
count is prone to races as the reference count is part of the mount =
Btw.: I'm not able to reproduce this error here -- what exactly is
your setup (amd configuration etc.)
J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig
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