From: Peter Zijlstra <peterz@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Eric Paris <eparis@redhat.com>,
linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org, hch@infradead.org,
zohar@us.ibm.com, warthog9@kernel.org, jmorris@namei.org,
kyle@mcmartin.ca, hpa@zytor.com, akpm@linux-foundation.org,
torvalds@linux-foundation.org, mingo@elte.hu,
viro@zeniv.linux.org.uk
Subject: Re: [PATCH 5/6] IMA: use rbtree instead of radix tree for inode information cache
Date: Wed, 20 Oct 2010 13:31:09 +0200 [thread overview]
Message-ID: <1287574269.3488.11.camel@twins> (raw)
In-Reply-To: <20101019231747.GC12506@dastard>
On Wed, 2010-10-20 at 10:17 +1100, Dave Chinner wrote:
> On Tue, Oct 19, 2010 at 06:58:39PM -0400, Eric Paris wrote:
> > @@ -36,12 +63,11 @@ struct ima_iint_cache *ima_iint_find_get(struct inode *inode)
> > struct ima_iint_cache *iint;
> >
> > rcu_read_lock();
> > - iint = radix_tree_lookup(&ima_iint_store, (unsigned long)inode);
> > - if (!iint)
> > - goto out;
> > - kref_get(&iint->refcount);
> > -out:
> > + iint = __ima_iint_find(inode);
> > + if (iint)
> > + kref_get(&iint->refcount);
> > rcu_read_unlock();
> > +
>
> This is wrong - the rbtree is protected only by the ima_iint_lock(),
> not RCU. Hence you can't do lockless lookups on an rbtree in this
> manner as they will race with inserts and deletes.
Correct, what can be made to work is combine RCU with a seqlock. Retry
the lookup using read_seqretry(), RCU here helps to ensure you're not
stepping on already freed memory.
So, tree modification does:
write_seqlock();
/* frob RB-tree, using call_rcu() for frees where needed */
write_sequnlock();
Lookup does:
unsigned seq;
rcu_read_lock()
again;
seq = read_seqbegin();
/* RB-tree lookup */
if (read_seqretry(seq))
goto again;
rcu_read_unlock();
return obj;
next prev parent reply other threads:[~2010-10-20 11:31 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-19 22:58 [PATCH 1/6] IMA: move read/write counters into struct inode Eric Paris
2010-10-19 22:58 ` [PATCH 2/6] IMA: drop the inode opencount since it isn't needed for operation Eric Paris
2010-10-19 22:58 ` [PATCH 3/6] IMA: use unsigned int instead of long for counters Eric Paris
2010-10-19 22:58 ` [PATCH 4/6] IMA: only allocate iint when needed Eric Paris
2010-10-20 3:53 ` Al Viro
2010-10-19 22:58 ` [PATCH 5/6] IMA: use rbtree instead of radix tree for inode information cache Eric Paris
2010-10-19 23:17 ` Dave Chinner
2010-10-20 11:31 ` Peter Zijlstra [this message]
2010-10-20 22:05 ` Dave Chinner
2010-10-20 22:22 ` Linus Torvalds
2010-10-20 22:47 ` Trond Myklebust
2010-10-21 0:58 ` Linus Torvalds
2010-10-21 2:17 ` Dave Chinner
2010-10-19 22:58 ` [PATCH 6/6] IMA: use i_writecount rather than a private counter Eric Paris
2010-10-20 0:25 ` [PATCH 1/6] IMA: move read/write counters into struct inode Linus Torvalds
2010-10-23 3:01 ` Eric Paris
2010-10-24 6:52 ` Mimi Zohar
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