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From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Christian Brauner <christian@brauner.io>,
	Jeff Layton <jlayton@kernel.org>,
	netfs@lists.linux.dev, v9fs@lists.linux.dev,
	linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] netfs: Fix netfs_page_mkwrite() to check folio->mapping is valid
Date: Mon, 24 Jun 2024 16:30:35 +0100	[thread overview]
Message-ID: <ZnmRGyuSZKtmJVhG@casper.infradead.org> (raw)
In-Reply-To: <614257.1719228181@warthog.procyon.org.uk>

On Mon, Jun 24, 2024 at 12:23:01PM +0100, David Howells wrote:
> @@ -508,6 +509,10 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
>  
>  	if (folio_lock_killable(folio) < 0)
>  		goto out;
> +	if (folio->mapping != mapping) {
> +		ret = VM_FAULT_NOPAGE | VM_FAULT_LOCKED;
> +		goto out;
> +	}

Have you tested this?  I'd expect it to throw some VM assertions.

        ret = vmf->vma->vm_ops->page_mkwrite(vmf);
        /* Restore original flags so that caller is not surprised */
        vmf->flags = old_flags;
        if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
                return ret;
...
                if (unlikely(!tmp || (tmp &
                                      (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
                        folio_put(folio);
                        return tmp;
                }

So you locked the folio, then called folio_put() without unlocking it.
Usually the VM complains noisily if you free a locked folio.

  reply	other threads:[~2024-06-24 15:30 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-06-24 11:23 [PATCH] netfs: Fix netfs_page_mkwrite() to check folio->mapping is valid David Howells
2024-06-24 15:30 ` Matthew Wilcox [this message]
2024-06-24 22:40 ` David Howells
2024-06-25 12:29 ` [PATCH v2] " David Howells
2024-06-25 14:54   ` Jeff Layton
2024-06-26 12:19   ` Christian Brauner

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