Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932971Ab2FAKR1 (ORCPT ); Fri, 1 Jun 2012 06:17:27 -0400 Received: from smtp.eu.citrix.com ([62.200.22.115]:38011 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759379Ab2FAKR0 (ORCPT ); Fri, 1 Jun 2012 06:17:26 -0400 X-IronPort-AV: E=Sophos;i="4.75,698,1330905600"; d="scan'208";a="12783130" Date: Fri, 1 Jun 2012 11:16:29 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball-desktop To: Konrad Rzeszutek Wilk CC: Jan Beulich , Stefano Stabellini , "axboe@kernel.dk" , "xen-devel@lists.xensource.com" , "linux-kernel@vger.kernel.org" Subject: Re: [Xen-devel] [PATCH 2/2] xen/blkfront: Add BUG_ON to deal with misbehaving backends. In-Reply-To: <20120531181712.GA19700@phenom.dumpdata.com> Message-ID: References: <1337982603-15692-1-git-send-email-konrad.wilk@oracle.com> <1337982603-15692-3-git-send-email-konrad.wilk@oracle.com> <4FC4A10F0200007800086842@nat28.tlf.novell.com> <20120531181712.GA19700@phenom.dumpdata.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3735 Lines: 97 On Thu, 31 May 2012, Konrad Rzeszutek Wilk wrote: > The blkfront_remove part is .. that is going to take some surgery to do > and I don't think I am going to be able to attempt that within the next couple > of weeks. So lets put that on the TODO list and just do this one? OK > >From 4aabb5b44778fc0c0b8d4f5a2e2cd8e8490064d7 Mon Sep 17 00:00:00 2001 > From: Konrad Rzeszutek Wilk > Date: Fri, 25 May 2012 17:34:51 -0400 > Subject: [PATCH] xen/blkfront: Add WARN to deal with misbehaving backends. > > Part of the ring structure is the 'id' field which is under > control of the frontend. The frontend stamps it with "some" > value (this some in this implementation being a value less > than BLK_RING_SIZE), and when it gets a response expects > said value to be in the response structure. We have a check > for the id field when spolling new requests but not when > de-spolling responses. > > We also add an extra check in add_id_to_freelist to make > sure that the 'struct request' was not NULL - as we cannot > pass a NULL to __blk_end_request_all, otherwise that crashes > (and all the operations that the response is dealing with > end up with __blk_end_request_all). > > Lastly we also print the name of the operation that failed. > > [v1: s/BUG/WARN/ suggested by Stefano] > [v2: Add extra check in add_id_to_freelist] > Signed-off-by: Konrad Rzeszutek Wilk > --- > drivers/block/xen-blkfront.c | 39 +++++++++++++++++++++++++++++---------- > 1 files changed, 29 insertions(+), 10 deletions(-) > > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c > index 60eed4b..c7ef8a4 100644 > --- a/drivers/block/xen-blkfront.c > +++ b/drivers/block/xen-blkfront.c > @@ -144,11 +144,22 @@ static int get_id_from_freelist(struct blkfront_info *info) > static void add_id_to_freelist(struct blkfront_info *info, > unsigned long id) > { > + BUG_ON(info->shadow[id].req.u.rw.id != id); > info->shadow[id].req.u.rw.id = info->shadow_free; > + BUG_ON(info->shadow[id].request == NULL); > info->shadow[id].request = NULL; > info->shadow_free = id; > } Like Jan said, it would be best to change the two BUG_ON into WARN_ON and return an error. > +static const char *op_name(int op) > +{ > + const char *names[BLKIF_OP_DISCARD+1] = { > + "read" , "write", "barrier", "flush", "reserved", "discard"}; > + > + if (op > BLKIF_OP_DISCARD) > + return "unknown"; > + return names[op]; > +} Considering that op is an int, shoudn't we check for negative values too? > static int xlbd_reserve_minors(unsigned int minor, unsigned int nr) > { > unsigned int end = minor + nr; > @@ -746,6 +757,18 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id) > > bret = RING_GET_RESPONSE(&info->ring, i); > id = bret->id; > + /* > + * The backend has messed up and given us an id that we would > + * never have given to it (we stamp it up to BLK_RING_SIZE - > + * look in get_id_from_freelist. > + */ > + if (id >= BLK_RING_SIZE) { > + /* We can't safely get the 'struct request' as > + * the id is busted. So limp along. */ > + WARN(1, "%s: response to %s has incorrect id (%d)!\n", > + info->gd->disk_name, op_name(bret->operation), id); > + continue; > + } > req = info->shadow[id].request; Do you think it would be better to goto error_out, instead of continue? I guess that depends on whether we expect the other requests to be in a good shape or not... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/