From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bob Liu Subject: Re: [PATCHv5 12/14] xen-blkback: safely unmap grants in case they are still in use Date: Mon, 09 Mar 2015 18:51:53 +0800 Message-ID: <54FD7B49.7080401@oracle.com> References: <1422377057-19221-1-git-send-email-david.vrabel@citrix.com> <1422377057-19221-13-git-send-email-david.vrabel@citrix.com> <54FD6331.8040503@oracle.com> <54FD6831.5020700@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YUvI8-0001dk-B2 for xen-devel@lists.xenproject.org; Mon, 09 Mar 2015 10:52:08 +0000 In-Reply-To: <54FD6831.5020700@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: David Vrabel Cc: xen-devel@lists.xenproject.org, Boris Ostrovsky , Jenny Herbert List-Id: xen-devel@lists.xenproject.org On 03/09/2015 05:30 PM, David Vrabel wrote: > On 09/03/15 09:09, Bob Liu wrote: >> Hi David, >> >> Recently I met an issue which is likely related with this patch. It >> happened when running block benchmark on domU, the backend was an iSCSI >> disk connected to dom0. I got below panic at put_page_testzero() on >> dom0, at that time the ixgbe network card was freeing skb pages in >> __skb_frag_unref() but the page->_count was already 0. >> Do you think is it possiable that page was already freed by blkback? > > It's possible, but in this case I think the blkback device must have > been destroyed for this to have happened, because blkback doesn't free > the pages until it is destroyed. > Sorry, I didn't get the point here, doesn't bio_complete free pages? E.g. __end_block_io_op() > xen_blkbk_unmap_and_respond() > put_free_pages() Then shrink_free_pagepool() free the page finally. I'm worry about there may be race condition some place and caused this panic, but it's hard to locate. It may exist in xen-blkback/grant or even the ixgbe network driver itself. > But in general networked block storage isn't safe without this patch. > That's true! Thanks, -Bob