From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 0F5706B004F for ; Thu, 12 Mar 2009 07:57:33 -0400 (EDT) Received: from d12nrmr1607.megacenter.de.ibm.com (d12nrmr1607.megacenter.de.ibm.com [9.149.167.49]) by mtagate3.de.ibm.com (8.14.3/8.13.8) with ESMTP id n2CBvUs4089964 for ; Thu, 12 Mar 2009 11:57:31 GMT Received: from d12av02.megacenter.de.ibm.com (d12av02.megacenter.de.ibm.com [9.149.165.228]) by d12nrmr1607.megacenter.de.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n2CBvUeL4321434 for ; Thu, 12 Mar 2009 12:57:30 +0100 Received: from d12av02.megacenter.de.ibm.com (loopback [127.0.0.1]) by d12av02.megacenter.de.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n2CBvThI003724 for ; Thu, 12 Mar 2009 12:57:30 +0100 Date: Thu, 12 Mar 2009 12:54:10 +0100 From: Martin Schwidefsky Subject: Re: [PATCH] acquire mmap semaphore in pagemap_read. Message-ID: <20090312125410.25400d18@skybase> In-Reply-To: <20090312114533.GA2407@x200.localdomain> References: <20090312113308.6fe18a93@skybase> <20090312114533.GA2407@x200.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Alexey Dobriyan Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matt Mackall , Gerald Schaefer , akpm@linux-foundation.org List-ID: On Thu, 12 Mar 2009 14:45:33 +0300 Alexey Dobriyan wrote: > On Thu, Mar 12, 2009 at 11:33:08AM +0100, Martin Schwidefsky wrote: > > --- linux-2.6/fs/proc/task_mmu.c > > +++ linux-2.6-patched/fs/proc/task_mmu.c > > @@ -716,7 +716,9 @@ static ssize_t pagemap_read(struct file > > * user buffer is tracked in "pm", and the walk > > * will stop when we hit the end of the buffer. > > */ > > + down_read(&mm->mmap_sem); > > ret = walk_page_range(start_vaddr, end_vaddr, &pagemap_walk); > > + up_read(&mm->mmap_sem); > > This will introduce "put_user under mmap_sem" which is deadlockable. Hmm, interesting. In this case the pagemap interface is fundamentally broken. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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