linux-kernel - Re: [PATCH 06/11] dax: Fix race between simultaneous faults

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Message-ID: <20150805114309.GA25784@node.dhcp.inet.fi>
Date:	Wed, 5 Aug 2015 14:43:09 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH 06/11] dax: Fix race between simultaneous faults

On Tue, Aug 04, 2015 at 03:58:00PM -0400, Matthew Wilcox wrote:
> diff --git a/mm/memory.c b/mm/memory.c
> index b94b587..5f46350 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2426,11 +2426,16 @@ void unmap_mapping_range(struct address_space *mapping,
>  		details.last_index = ULONG_MAX;
>  
>  
> -	/* DAX uses i_mmap_lock to serialise file truncate vs page fault */
> -	i_mmap_lock_write(mapping);
> +	/*
> +	 * DAX already holds i_mmap_lock to serialise file truncate vs
> +	 * page fault and page fault vs page fault.
> +	 */
> +	if (!IS_DAX(mapping->host))
> +		i_mmap_lock_write(mapping);
>  	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap)))
>  		unmap_mapping_range_tree(&mapping->i_mmap, &details);
> -	i_mmap_unlock_write(mapping);
> +	if (!IS_DAX(mapping->host))
> +		i_mmap_unlock_write(mapping);
>  }
>  EXPORT_SYMBOL(unmap_mapping_range);

Huh? What protects mapping->i_mmap here? I don't see anything up by stack
taking the lock.

-- 
 Kirill A. Shutemov
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