linux-kernel - Re: [PATCH v2] vfs: don't unnecessarily clone write access for writable fds

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Message-ID: <20200629165014.GA20492@sol.localdomain>
Date:   Mon, 29 Jun 2020 09:50:14 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Daeho Jeong <daeho43@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] vfs: don't unnecessarily clone write access for
 writable fds

On Thu, Jun 11, 2020 at 09:05:34AM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> There's no need for mnt_want_write_file() to increment mnt_writers when
> the file is already open for writing, provided that
> mnt_drop_write_file() is changed to conditionally decrement it.
> 
> We seem to have ended up in the current situation because
> mnt_want_write_file() used to be paired with mnt_drop_write(), due to
> mnt_drop_write_file() not having been added yet.  So originally
> mnt_want_write_file() had to always increment mnt_writers.
> 
> But later mnt_drop_write_file() was added, and all callers of
> mnt_want_write_file() were paired with it.  This makes the compatibility
> between mnt_want_write_file() and mnt_drop_write() no longer necessary.
> 
> Therefore, make __mnt_want_write_file() and __mnt_drop_write_file() skip
> incrementing mnt_writers on files already open for writing.  This
> removes the only caller of mnt_clone_write(), so remove that too.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Al, any thoughts on this patch?

- Eric