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From: Al Viro <viro@zeniv.linux.org.uk>
To: Gautham Ananthakrishna <gautham.ananthakrishna@oracle.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, matthew.wilcox@oracle.com,
	khlebnikov@yandex-team.ru
Subject: Re: [PATCH RFC 1/6] dcache: sweep cached negative dentries to the end of list of siblings
Date: Thu, 15 Apr 2021 16:50:56 +0000	[thread overview]
Message-ID: <YHhu8PvSOkwkUqW7@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <YHZa4PWnWfUqkARi@zeniv-ca.linux.org.uk>

On Wed, Apr 14, 2021 at 03:00:48AM +0000, Al Viro wrote:

> Ugh...  So when dput() drives the refcount down to 0 you hit lock_parent()
> and only then bother to check if the sucker had been negative in the first
                                              ^^^^^^^^^^^^^^^^^
                                              had zero refcount, of course.
> place?

> > @@ -1970,6 +2021,8 @@ void d_instantiate(struct dentry *entry, struct inode * inode)
> >  {
> >  	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
> >  	if (inode) {
> > +		if (d_is_tail_negative(entry))
> > +			recycle_negative(entry);
> >  		security_d_instantiate(entry, inode);
> >  		spin_lock(&inode->i_lock);
> >  		__d_instantiate(entry, inode);
> 
> Wait a bloody minute.  What about d_instantiate_new() right next to it?

Another fun question: where's the proof that __d_add(dentry, non_NULL_inode)
won't happen to dentry marked tail-negative?  From a quick grep I see at
least one such place - on success cifs_do_create() does
        d_drop(direntry);
	d_add(direntry, newinode);
and it would bloody well evade what you are doing in d_instantiate().
Same seems to be true for nfs_link()...

  reply	other threads:[~2021-04-15 16:51 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-21 13:19 [PATCH RFC 0/6] fix the negative dentres bloating system memory usage Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 1/6] dcache: sweep cached negative dentries to the end of list of siblings Gautham Ananthakrishna
2021-04-14  3:00   ` Al Viro
2021-04-15 16:50     ` Al Viro [this message]
2021-04-14  3:41   ` Al Viro
2021-04-15 16:25     ` Al Viro
2021-01-21 13:19 ` [PATCH RFC 2/6] fsnotify: stop walking child dentries if remaining tail is negative Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 3/6] dcache: add action D_WALK_SKIP_SIBLINGS to d_walk() Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 4/6] dcache: stop walking siblings if remaining dentries all negative Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 5/6] dcache: push releasing dentry lock into sweep_negative Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 6/6] dcache: prevent flooding with negative dentries Gautham Ananthakrishna
2021-04-14  3:56   ` Al Viro
2021-03-31 14:23 ` [PATCH RFC 0/6] fix the negative dentres bloating system memory usage Matthew Wilcox
2021-04-14  2:40 ` Al Viro

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