From: Nick Piggin <npiggin@gmail.com>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: lifetime of DCACHE_DISCONECTED dentries
Date: Tue, 16 Nov 2010 17:45:03 +1100 [thread overview]
Message-ID: <AANLkTim1QjTwOZ4SHdMy8Y6TOAnaOYtTwgwHXfH5H5Xn@mail.gmail.com> (raw)
In-Reply-To: <20101115174837.GB10044@fieldses.org>
On Tue, Nov 16, 2010 at 4:48 AM, J. Bruce Fields <bfields@fieldses.org> wrote:
> On Sat, Nov 13, 2010 at 10:53:12PM +1100, Nick Piggin wrote:
>> On Sat, Nov 13, 2010 at 5:43 AM, J. Bruce Fields <bfields@fieldses.org> wrote:
>> > - putfh: look up the filehandle. The only alias found for the
>> > inode will be DCACHE_UNHASHED alias referenced by the filp
>> > associated with the nfsd open. d_obtain_alias() doesn't like
>> > this, so it creates a new DCACHE_DISCONECTED dentry and
>> > returns that instead.
>>
>> This seems to be where the thing goes wrong. It isn't a hashed dentry at
>> this point here, so d_obtain_alias should not be making one.
>
> Sounds sensible. (But can you think of any actual bugs that will result
> from trying to add a new hashed dentry in this case?)
Well, this one? :)
>> I think the inode i_nlink games are much more appropriate on this side of
>> the equation, rather than the dput side (after all, d_obtain_alias is setting
>> up an alias for the inode).
>>
>> Can you even put the link check into __d_find_alias?
>>
>> - if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
>> + if (S_ISDIR(inode->i_mode) || !inode->i_nlink ||
>> !d_unhashed(alias)) {
>>
>> Something like that?
>
> The immediate result of that would be for the close rpc (or any rpc's
> sent after the file was unlinked) to fail with ESTALE.
Why is that? Seems like it would be a bug, because a hashed dentry may
be unhashed at any time concurrently to nfsd operation, so it should be
able to tolerate that so long as it has a ref on the inode?
> But nfsd already holds an open file in this case, and you could argue
> that it should be using that from the start.
Yes.
> So, we could modify nfsd to add a hash mapping filehandles to the filp's
> that it knows about, and have nfsd consult that hash before calling
> dentry_to_fh.
Could be an option. It would be a pity not just be able to use the alias list.
What exactly goes wrong when it gets an unhashed alias back?
next prev parent reply other threads:[~2010-11-16 6:45 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-12 18:43 lifetime of DCACHE_DISCONECTED dentries J. Bruce Fields
2010-11-13 11:53 ` Nick Piggin
2010-11-15 17:48 ` J. Bruce Fields
2010-11-16 6:45 ` Nick Piggin [this message]
2010-11-29 3:56 ` Nick Piggin
2010-11-29 19:32 ` J. Bruce Fields
2010-11-30 1:00 ` Nick Piggin
2010-11-30 18:39 ` J. Bruce Fields
2010-12-03 22:33 ` [PATCH] nfsd4: allow __d_obtain_alias() to return unhashed dentries J. Bruce Fields
2010-12-13 5:19 ` Nick Piggin
2010-12-14 22:01 ` J. Bruce Fields
2010-12-17 17:53 ` [PATCH] fs/dcache: use standard list macro for d_find_alias J. Bruce Fields
2010-12-17 18:00 ` [PATCH 2/2] fs/dcache: allow __d_obtain_alias() to return unhashed dentries J. Bruce Fields
2010-12-18 2:01 ` Nick Piggin
2010-12-18 16:16 ` J. Bruce Fields
2010-12-19 14:53 ` Nick Piggin
2010-12-27 23:46 ` [PATCH] " J. Bruce Fields
2011-01-18 20:45 ` J. Bruce Fields
2011-01-18 22:02 ` Nick Piggin
2011-01-18 22:08 ` J. Bruce Fields
2011-03-08 18:13 ` J. Bruce Fields
2011-03-10 10:58 ` Al Viro
2011-03-11 4:07 ` NeilBrown
2012-02-14 17:03 ` J. Bruce Fields
2012-02-15 16:56 ` J. Bruce Fields
2012-02-16 3:06 ` NeilBrown
2012-02-16 11:51 ` J. Bruce Fields
2012-02-16 16:08 ` J. Bruce Fields
2012-02-16 22:30 ` J. Bruce Fields
2012-02-17 16:34 ` Peng Tao
2012-03-13 20:55 ` J. Bruce Fields
2012-03-13 20:58 ` [PATCH 1/2] vfs: stop d_splice_alias creating directory aliases J. Bruce Fields
2012-03-13 20:58 ` [PATCH 2/2] vfs: remove unused __d_splice_alias argument J. Bruce Fields
2012-02-20 2:55 ` [PATCH] fs/dcache: allow __d_obtain_alias() to return unhashed dentries NeilBrown
2012-02-29 23:10 ` J. Bruce Fields
2012-06-28 13:59 ` J. Bruce Fields
2012-06-29 20:10 ` J. Bruce Fields
2012-06-29 20:29 ` J. Bruce Fields
2012-07-01 23:15 ` NeilBrown
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