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In-Reply-To: <E1NBZJ5-0003hL-Qc@longford.logfs.org>
References: <20091120181113.GA2159@logfs.org>
	 <E1NBZJ5-0003hL-Qc@longford.logfs.org>
Date: Mon, 23 Nov 2009 14:33:15 +0200
Message-ID: <84144f020911230433q5fd90321m9b463cb425fafe7d@mail.gmail.com>
Subject: Re: [PATCH 12/17] [LogFS] readwrite.c
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Joern Engel <joern@logfs.org>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
       linux-mtd@lists.infradead.org, Arnd Bergmann <arnd@arndb.de>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>,
       Andrew Morton <akpm@linux-foundation.org>
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Lines: 38

Hi Joern,

(Dunno who to CC, really, so lets see if I can trick Andrew or Hugh
into looking at the issue.)

On Fri, Nov 20, 2009 at 9:38 PM, Joern Engel <joern@logfs.org> wrote:
> +static void logfs_lock_write_page(struct page *page)
> +{
> + ? ? ? int loop = 0;
> +
> + ? ? ? while (unlikely(!trylock_page(page))) {
> + ? ? ? ? ? ? ? if (loop++ > 0x1000) {
> + ? ? ? ? ? ? ? ? ? ? ? /* Has been observed once so far... */
> + ? ? ? ? ? ? ? ? ? ? ? printk(KERN_ERR "stack at %p\n", &loop);
> + ? ? ? ? ? ? ? ? ? ? ? BUG();
> + ? ? ? ? ? ? ? }
> + ? ? ? ? ? ? ? if (PagePreLocked(page)) {
> + ? ? ? ? ? ? ? ? ? ? ? /* Holder of page lock is waiting for us, it
> + ? ? ? ? ? ? ? ? ? ? ? ?* is safe to use this page. */
> + ? ? ? ? ? ? ? ? ? ? ? break;
> + ? ? ? ? ? ? ? }
> + ? ? ? ? ? ? ? /* Some other process has this page locked and has
> + ? ? ? ? ? ? ? ?* nothing to do with us. ?Wait for it to finish.
> + ? ? ? ? ? ? ? ?*/
> + ? ? ? ? ? ? ? schedule();
> + ? ? ? }
> + ? ? ? BUG_ON(!PageLocked(page));
> +}

What's the purpose of PagePreLocked()? The above function looks pretty
fragile for a filesystem to me.

                        Pekka
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