linux-ext4 - Re: [PATCH 01/34] namespace: take lock_mount

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Message-ID: <20201101144108.GA23378@infradead.org>
Date:   Sun, 1 Nov 2020 14:41:08 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org,
        John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Geoffrey Thomas <geofft@...reload.com>,
        Mrunal Patel <mpatel@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
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        Amir Goldstein <amir73il@...il.com>,
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        Seth Forshee <seth.forshee@...onical.com>,
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        containers@...ts.linux-foundation.org,
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Subject: Re: [PATCH 01/34] namespace: take lock_mount_hash() directly when
 changing flags

> index cebaa3e81794..20ee291a7af4 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -463,7 +463,6 @@ static int mnt_make_readonly(struct mount *mnt)
>  {
>  	int ret = 0;
>  
> -	lock_mount_hash();

What about adding a lockdep_assert_lock_held in all the functions
that used to take the lock to document the assumptions?

>  static int __mnt_unmake_readonly(struct mount *mnt)
>  {
> -	lock_mount_hash();
>  	mnt->mnt.mnt_flags &= ~MNT_READONLY;
> -	unlock_mount_hash();
>  	return 0;

This helper is rather pointless now.

>  static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
>  {
> -	lock_mount_hash();
>  	mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
>  	mnt->mnt.mnt_flags = mnt_flags;
>  	touch_mnt_namespace(mnt->mnt_ns);
> -	unlock_mount_hash();

In linux-next there is an additional notify_mount after the unlock here.

Also while you touch this lock_mount_hash/unlock_mount_hash could be
moved to namespace.c and maked static now.