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	Fri, 16 Oct 2026 18:29:27 +0000
Date: Fri, 16 Oct 2026 19:29:27 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: Zhao Gongyi <zhaogongyi@bytedance.com>
Cc: brauner@kernel.org, jack@suse.cz, jlayton@kernel.org, cel@kernel.org,
	neil@brown.name, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] vfs: keep the mount pinned while waiting for a parent
 delegation break
Message-ID: <20261016182927.GG989762@ZenIV>
References: <20261016093421.90725-1-zhaogongyi@bytedance.com>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Fri, Oct 16, 2026 at 05:34:21PM +0800, Zhao Gongyi wrote:
> filename_mknodat(), filename_mkdirat(), filename_symlinkat() and
> filename_rmdir() can call break_deleg_wait() on a delegated parent
> directory after dropping the struct path that pins the mount.
> try_break_deleg() only takes an inode reference, and an inode reference
> does not keep the superblock active.

So why not have it acquire an active superblock reference at the
same time?  We don't need struct mount reference there - all it
takes in increment of inode->i_sb->s_active on try_break_deleg()
side and deactivate_super() on ->i_sb fetched *before* iput()
of ->di_inode on the break_deleg_wait() side...

No need to mess with every user of that thing...