linux-kernel - Re: [patch 10/10] mm: fix pagecache write deadlocks

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Message-ID: <45A9AAAB.2090008@yahoo.com.au>
Date:	Sun, 14 Jan 2007 14:59:39 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Nick Piggin <npiggin@...e.de>
CC:	Linux Memory Management <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Filesystems <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [patch 10/10] mm: fix pagecache write deadlocks

Nick Piggin wrote:

> @@ -1878,31 +1889,88 @@ generic_file_buffered_write(struct kiocb
>  			break;
>  		}
>  
> +		/*
> +		 * non-uptodate pages cannot cope with short copies, and we
> +		 * cannot take a pagefault with the destination page locked.
> +		 * So pin the source page to copy it.
> +		 */
> +		if (!PageUptodate(page)) {
> +			unlock_page(page);
> +
> +			bytes = min(bytes, PAGE_CACHE_SIZE -
> +				     ((unsigned long)buf & ~PAGE_CACHE_MASK));
> +
> +			/*
> +			 * Cannot get_user_pages with a page locked for the
> +			 * same reason as we can't take a page fault with a
> +			 * page locked (as explained below).
> +			 */
> +			status = get_user_pages(current, current->mm,
> +					(unsigned long)buf & PAGE_CACHE_MASK, 1,
> +					0, 0, &src_page, NULL);

Thinko... get_user_pages needs to be called with mmap_sem held, obviously.

-- 
SUSE Labs, Novell Inc.
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