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

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Message-ID: <20200916035914.GA825@sol.localdomain>
Date:   Tue, 15 Sep 2020 20:59:14 -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 Mon, Jun 29, 2020 at 09:50:14AM -0700, Eric Biggers wrote:
> 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?
> 

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