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

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Message-ID: <20190411022514.GC2217@ZenIV.linux.org.uk>
Date:   Thu, 11 Apr 2019 03:25:15 +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 04:15:48PM -0700, Eric Biggers wrote:
> On Wed, Apr 10, 2019 at 10:06:57PM +0100, Al Viro wrote:
> > 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()...
> 
> How so?  The patch already updates vfs_readlink().

Huh?  Right you are - fsck knows how have I managed to misread that...
Anyway, I can pick that READ_ONCE() patch through vfs.git if you wish,
or it can go through your tree with my Acked-by - up to you...