linux-kernel - Re: [PATCH 12/13] XFS: allow follow_link to often succeed in RCU-walk.

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Message-ID: <20150316223758.GE29656@ZenIV.linux.org.uk>
Date:	Mon, 16 Mar 2015 22:37:58 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	NeilBrown <neilb@...e.de>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/13] XFS: allow follow_link to often succeed in
 RCU-walk.

On Mon, Mar 16, 2015 at 03:43:20PM +1100, NeilBrown wrote:

> -	xfs_ilock(ip, XFS_ILOCK_SHARED);
> +	if (rcu) {
> +		if (xfs_ilock_nowait(ip, XFS_ILOCK_SHARED) == 0)
> +			return -ECHILD;

Umm...  Is that guaranteed to be safe for inode that is currently going
through xfs ->evict_inode()?  struct inode getting freed is RCU-delayed;
->evict_inode() is *not*.  It can happen right under you in RCU pathwalk.
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