From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: Checkin 7404ad3b6d04efbd918e9e2e776bf560fbedf47d breaks boot on KVM Date: Tue, 14 Oct 2008 14:35:42 -0400 Message-ID: <1224009342.12440.18.camel@localhost.localdomain> References: <48F3E1C9.6030007@zytor.com> <1223990609.12440.8.camel@localhost.localdomain> <48F4DF3E.2050903@zytor.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from accolon.hansenpartnership.com ([76.243.235.52]:59005 "EHLO accolon.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751390AbYJNSgF (ORCPT ); Tue, 14 Oct 2008 14:36:05 -0400 In-Reply-To: <48F4DF3E.2050903@zytor.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: "H. Peter Anvin" Cc: Linux Kernel Mailing List , linux-scsi On Tue, 2008-10-14 at 11:04 -0700, H. Peter Anvin wrote: > James Bottomley wrote: > >> > >> :040000 040000 98fc7ae95211b8d16e2e8ca46997be660ad9ba93 > >> 2d35d0a2b6232411b840a9ccf6a52b946172566e M drivers > >> > >> However, simply reverting this commit caused a panic on boot (not > >> entirely surprising.) > > > > Actually, it is surprising. That patch takes the default arithmetic for > > calculating the disk size out of sd and uses a routine to do it more > > efficiently in lib/string_helpers.c > > > > So there are two problems: Why does it panic on revert (could you post > > the oops) and what does kvm object to in string_get_size ... it's a > > fairly innocuous routine as I read it ... your symptoms sound like the > > for loop isn't terminating. > > > > Looks like it's trying to print a zero. I made a diff to print out the > raw numbers, and did indeed get zero. > > Now, *why* it is printing a zero is another matter (as is why using > ffz() instead of ilog2() there...). Some quick investigation showed > that sdkp->capacity is a 32-bit quantity in this configuration, and > shifting it left by 9 of course ends up with zero; being a virtual disk, > it's an exact power of two. > > Still, it is bad that string_get_size() hangs on passing zero. > > The spinlock lockup is still happening, so I'm assuming it is an > unrelated bug that was masked by the string_get_size issue. > > Patch series will follow shortly. Does this fix it? James --- diff --git a/lib/string_helpers.c b/lib/string_helpers.c index 8347925..b5acbe9 100644 --- a/lib/string_helpers.c +++ b/lib/string_helpers.c @@ -45,7 +45,7 @@ int string_get_size(u64 size, const enum string_size_units units, remainder = do_div(size, divisor[units]); sf_cap = size; - for (j = 0; sf_cap*10 < 1000; j++) + for (j = 0; sf_cap != 0 && sf_cap*10 < 1000; j++) sf_cap *= 10; if (j) {