linux-kernel - Re: More parallel atomic_open/d_splice_alias fun with NFS and possibly more FSes.

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Message-Id: <6334F6B6-807C-4B36-B785-7DD502E0D70B@linuxhacker.ru>
Date:	Tue, 5 Jul 2016 23:25:46 -0400
From:	Oleg Drokin <green@...uxhacker.ru>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Mailing List <linux-kernel@...r.kernel.org>,
	"<linux-fsdevel@...r.kernel.org>" <linux-fsdevel@...r.kernel.org>
Subject: Re: More parallel atomic_open/d_splice_alias fun with NFS and possibly more FSes.


On Jul 5, 2016, at 11:20 PM, Al Viro wrote:

> On Tue, Jul 05, 2016 at 08:29:37PM -0400, Oleg Drokin wrote:
>>> +		/* Otherwise we just unhash it to be rehashed afresh via
>>> +		 * lookup if necessary
>>> +		 */
>>> +		d_drop(dentry);
>> 
>> So we can even drop this part and retain the top condition as it was.
>> d_add does not care if the dentry we are feeding it was hashed or not,
>> so do you see any downsides to doing that I wonder?
> 
> d_add() on hashed dentry will end up reaching this:
> static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
> {
>        BUG_ON(!d_unhashed(entry));

Ah, ok. Yes, I remember about it now from the older issue with nfs.

It's still puzzling why I did not hit it yet, but oh well.

I wonder if handling of negative dentries broke… Time for more investigations.