From: Greg Banks <gnb@melbourne.sgi.com>
To: Neil Brown <neilb@cse.unsw.edu.au>
Cc: Nikita Danilov <Nikita@Namesys.COM>,
linux kernel mailing list <linux-kernel@vger.kernel.org>,
alexander viro <viro@parcelfarce.linux.theplanet.co.uk>,
trond myklebust <trondmy@trondhjem.org>
Subject: Re: d_splice_alias() problem.
Date: Tue, 04 May 2004 17:00:15 +1000 [thread overview]
Message-ID: <40973F7F.A9FA4F1@melbourne.sgi.com> (raw)
In-Reply-To: 16534.54704.792101.617408@cse.unsw.edu.au
Neil Brown wrote:
>
> > * Dentry_stat.nr_unused can be be spuriously decremented when dput()
> > races with __dget_unlocked(). Eventual result is nr_unused<0
> > and kswapd loops. This is the problem I mentioned earlier. Note
> > that this is not an NFS-specific problem. Fix is:
> >
> > --- linux.orig/fs/dcache.c Mon May 3 21:46:30 2004
> > +++ linux/fs/dcache.c Mon May 3 21:49:07 2004
> > @@ -255,8 +255,8 @@
> >
> > static inline struct dentry * __dget_locked(struct dentry *dentry)
> > {
> > - atomic_inc(&dentry->d_count);
> > - if (atomic_read(&dentry->d_count) == 1) {
> > + if (atomic_inc(&dentry->d_count) == 1) {
>
> One problem with this is that (in include/asm-i386/atomic.h at least):
> static __inline__ void atomic_inc(atomic_t *v)
Ok, how about this...it's portable, and not racy, but may perturb the
logic slightly by also taking dentries off the unused list in the case
where they already had d_count>=1. I'm not sure how significant that is.
In any case this also passes my tests.
--- linux.orig/fs/dcache.c Mon May 3 21:46:30 2004
+++ linux/fs/dcache.c Tue May 4 14:34:44 2004
@@ -256,7 +256,7 @@
static inline struct dentry * __dget_locked(struct dentry *dentry)
{
atomic_inc(&dentry->d_count);
- if (atomic_read(&dentry->d_count) == 1) {
+ if (!list_empty(&dentry->d_lru)) {
dentry_stat.nr_unused--;
list_del_init(&dentry->d_lru);
}
@@ -663,6 +663,7 @@
if (gfp_mask & __GFP_FS)
prune_dcache(nr);
}
+ BUG_ON(dentry_stat.nr_unused < 0);
return dentry_stat.nr_unused;
}
Greg.
--
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
I don't speak for SGI.
next prev parent reply other threads:[~2004-05-04 7:01 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-04-23 13:02 d_splice_alias() problem Nikita Danilov
2004-04-23 15:40 ` Andreas Dilger
2004-04-23 16:20 ` Nikita Danilov
2004-04-23 23:49 ` Andrew Morton
2004-04-26 12:45 ` Nikita Danilov
2004-04-30 4:54 ` Neil Brown
2004-04-30 7:50 ` Greg Banks
2004-04-30 13:28 ` Nikita Danilov
2004-05-03 23:46 ` Neil Brown
2004-05-03 12:02 ` Greg Banks
2004-05-03 23:28 ` Neil Brown
2004-05-04 0:05 ` Greg Banks
2004-05-04 7:00 ` Greg Banks [this message]
2004-05-04 9:46 ` viro
2004-05-04 10:21 ` Greg Banks
2004-05-05 0:11 ` Neil Brown
2004-05-10 3:03 ` Neil Brown
2004-05-10 4:50 ` Greg Banks
2004-05-10 3:27 ` Neil Brown
2004-05-10 11:28 ` Greg Banks
2004-05-13 5:58 ` Neil Brown
2004-05-13 7:15 ` Greg Banks
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