linux-ext4 - Re: [PATCH v2 1/2] vfs: use READ_ONCE() to access ->i

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Message-ID: <20190410210657.GA2217@ZenIV.linux.org.uk>
Date:   Wed, 10 Apr 2019 22:06:57 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-mtd@...ts.infradead.org
Subject: Re: [PATCH v2 1/2] vfs: use READ_ONCE() to access ->i_link

On Wed, Apr 10, 2019 at 01:21:14PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Use 'READ_ONCE(inode->i_link)' to explicitly support filesystems caching
> the symlink target in ->i_link later if it was unavailable at iget()
> time, or wasn't easily available.  I'll be doing this in fscrypt, to
> improve the performance of encrypted symlinks on ext4, f2fs, and ubifs.
> 
> ->i_link will start NULL and may later be set to a non-NULL value by a
> smp_store_release() or cmpxchg_release().  READ_ONCE() is needed on the
> read side.  smp_load_acquire() is unnecessary because only a data
> dependency barrier is required.  (Thanks to Al for pointing this out.)

You've missed vfs_readlink()...