From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 50EDD6B0055 for ; Sun, 31 May 2009 13:05:41 -0400 (EDT) Date: Sun, 31 May 2009 10:05:36 -0700 (PDT) From: Linus Torvalds Subject: Re: [PATCH] Use kzfree in tty buffer management to enforce data sanitization In-Reply-To: <20090531112630.2c7f4f1d@lxorguk.ukuu.org.uk> Message-ID: References: <20090531015537.GA8941@oblivion.subreption.com> <84144f020905302324r5e342f2dlfd711241ecfc8374@mail.gmail.com> <20090531112630.2c7f4f1d@lxorguk.ukuu.org.uk> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-14 Content-Transfer-Encoding: 8BIT Sender: owner-linux-mm@kvack.org To: Alan Cox Cc: Pekka Enberg , "Larry H." , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Rik van Riel List-ID: On Sun, 31 May 2009, Alan Cox wrote: > > > memset(buf->data, 0, N_TTY_BUF_SIZE); > > > if (PAGE_SIZE != N_TTY_BUF_SIZE) > > > kfree(...) > > > else > > > free_page(...) > > > > > > > > > but quite frankly, I'm not convinced about these patches at all. > > > > I wonder why the tty code has that N_TTY_BUF_SIZE special casing in > > the first place? I think we can probably just get rid of it and thus > > we can use kzfree() here if we want to. > > Some platforms with very large page sizes override the use of page based > allocators (eg older ARM would go around allocating 32K). The normal path > is 4K or 8K page sized buffers. I think Pekka meant the other way around - why don't we always just use kmalloc(N_TTY_BUF_SIZE)/kfree(), and drop the whole conditional "use page allocator" entirely? I suspect the "use page allocator" is historical - ie the tty layer originally always did that, and then when people wanted to suppotr smaller areas than one page, they added the special case. I have this dim memory of the _original_ kmalloc not handling page-sized allocations well (due to embedded size/pointer overheads), but I think all current allocators are perfectly happy to allocate PAGE_SIZE buffers without slop. If I'm right, then we could just use kmalloc/kfree unconditionally. Pekka? Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org