linux-kernel - Re: [PATCH 2/3] xfs: convert perag lookup to xarray

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Message-ID: <ZrpcTAuJFSzE4-nA@casper.infradead.org>
Date: Mon, 12 Aug 2024 20:02:36 +0100
From: Matthew Wilcox <willy@...radead.org>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: Christoph Hellwig <hch@....de>,
	Chandan Babu R <chandan.babu@...cle.com>,
	"Darrick J. Wong" <djwong@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, p.raghav@...sung.com
Subject: Re: [PATCH 2/3] xfs: convert perag lookup to xarray

On Mon, Aug 12, 2024 at 04:39:56PM +0000, Pankaj Raghav (Samsung) wrote:
> On Mon, Aug 12, 2024 at 08:31:01AM +0200, Christoph Hellwig wrote:
> > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> > index 7e80732cb54708..5efb1e8b4107a9 100644
> > --- a/fs/xfs/libxfs/xfs_ag.c
> > +++ b/fs/xfs/libxfs/xfs_ag.c
> > @@ -46,7 +46,7 @@ xfs_perag_get(
> >  	struct xfs_perag	*pag;
> >  
> >  	rcu_read_lock();
> xa_load() already calls rcu_read_lock(). So we can get rid of this I
> guess?

Almost certainly not; I assume pag is RCU-freed, so you'd be introducing
a UAF if the RCU lock is dropped before getting a refcount on the pag.