From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from zimbra13.linbit.com (zimbra.linbit.com [212.69.161.123]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by mail09.linbit.com (LINBIT Mail Daemon) with ESMTPS id F0E4B105059D for ; Fri, 13 Mar 2015 00:08:13 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by zimbra13.linbit.com (Postfix) with ESMTP id EDCB044D30A for ; Fri, 13 Mar 2015 00:08:13 +0100 (CET) Received: from zimbra13.linbit.com ([127.0.0.1]) by localhost (zimbra13.linbit.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id z2AT91jjKPsH for ; Fri, 13 Mar 2015 00:08:13 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by zimbra13.linbit.com (Postfix) with ESMTP id CB33C44D391 for ; Fri, 13 Mar 2015 00:08:13 +0100 (CET) Received: from zimbra13.linbit.com ([127.0.0.1]) by localhost (zimbra13.linbit.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id AfAMsHVh-00x for ; Fri, 13 Mar 2015 00:08:13 +0100 (CET) Received: from soda.linbit (tuerlsteher.linbit.com [86.59.100.100]) by zimbra13.linbit.com (Postfix) with ESMTPS id A1ABB44D30A for ; Fri, 13 Mar 2015 00:08:13 +0100 (CET) Resent-Message-ID: <20150312230813.GR3961@soda.linbit> Message-ID: <54FBA9A3.9070606@fb.com> Date: Sat, 7 Mar 2015 18:45:07 -0700 From: Jens Axboe MIME-Version: 1.0 To: David Rientjes References: <54FB98F3.2050308@fb.com> <54FB9FE2.5040707@fb.com> In-Reply-To: Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, drbd-user@lists.linbit.com, Lars Ellenberg Subject: Re: [Drbd-dev] [patch 1/2] block, drbd: fix drbd_req_new() initialization List-Id: "*Coordination* of development, patches, contributions -- *Questions* \(even to developers\) go to drbd-user, please." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 03/07/2015 06:27 PM, David Rientjes wrote: > On Sat, 7 Mar 2015, Jens Axboe wrote: > >>>>> mempool_alloc() does not support __GFP_ZERO since elements may come from >>>>> memory that has already been released by mempool_free(). >>>>> >>>>> Remove __GFP_ZERO from mempool_alloc() in drbd_req_new() and properly >>>>> initialize it to 0. >>>> >>>> You should add it to mempool instead, avoid having this issue show up for >>>> other folks as well. It'd be trivial to do. Normal ->alloc() should honor >>>> __GFP_ZERO, just do the same manually for removing an item from the internal >>>> pool. >>>> >>> >>> Umm, it's not trivial to do and wouldn't make sense to do it. Mempools >> >> Uhm, it would make sense, though. >> > > Disagree, I don't think we should extend mempool to know the element size, > modify every user of mempool to pass it in, and keep it consistent with > mempool_alloc_t for the benefit of __GFP_ZERO for this one buggy caller. > Most users don't need __GFP_ZERO and just overwrite the entire element > after mempool_alloc() and it would be an unnecessary overhead to even > check for the bit set. So it wouldn't make sense in terms of performance > or maintainability. My point is that conceptually, of course it makes sense to do and it _should_ do it. We don't have the size, too bad, I don't disagree that adding it just for this is necessarily the best idea. >>> don't know the element size, in other words it wouldn't know the length to >>> memset() to 0 for mempool_alloc(). It shouldn't be modified to know the >>> element size since elements are allocated by the implementation of >>> mempool_alloc_t and they could easily become inconsistent. This patch is >>> what you want to merge, really. >>> >> >> I forgot we don't have the size in there. Then I would suggest adding a >> WARN_ON() for __GFP_ZERO being set in mempool_alloc(), at the very least. >> > > There is, it's a VM_WARN_ON_ONCE() that will show up if you configure > CONFIG_DEBUG_VM. OK, that's good enough then. -- Jens Axboe