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Date:   Fri, 19 Feb 2021 04:11:05 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Denis Kirjanov <kda@linux-powerpc.org>
Cc:     Christoph Hellwig <hch@infradead.org>,
        linux-kernel@vger.kernel.org, Jakub Kicinski <kuba@kernel.org>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] fs: export kern_path_locked
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On Tue, Feb 16, 2021 at 06:00:34PM +0000, Al Viro wrote:

> Sigh...  OK, so we want something like
> 	user_path_create()
> 	vfs_mknod()
> 	created = true
> 	grab bindlock
> 	....
> 	drop bindlock
> 	if failed && created
> 		vfs_unlink()
> 	done_path_create()	
> in unix_bind()...  That would push ->bindlock all way down in the hierarchy,
> so that should be deadlock-free, but it looks like that'll be fucking ugly ;-/
> 
> Let me try and play with that a bit, maybe it can be massaged to something
> relatively sane...

OK...  Completely untested series follows.  Preliminary massage in first
6 patches, then actual "add cleanup on failure", then minor followup
cleanup.
      af_unix: take address assignment/hash insertion into a new helper
      unix_bind(): allocate addr earlier
      unix_bind(): separate BSD and abstract cases
      unix_bind(): take BSD and abstract address cases into new helpers
      fold unix_mknod() into unix_bind_bsd()
      unix_bind_bsd(): move done_path_create() call after dealing with ->bindlock
      unix_bind_bsd(): unlink if we fail after successful mknod
      __unix_find_socket_byname(): don't pass hash and type separately

Branch is in git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #misc.af_unix,
individual patches in followups