From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [RFC][PATCH] walking the page lists needs the page_alloc lock Date: Fri, 13 Aug 2010 07:40:23 +0100 Message-ID: <4C6504F7020000780000FA8C@vpn.id2.novell.com> References: <20100723134913.GQ13291@whitby.uk.xensource.com> <4C642AC4020000780000F8D8@vpn.id2.novell.com> <20100812163712.GA20252@whitby.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20100812163712.GA20252@whitby.uk.xensource.com> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Tim Deegan Cc: "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org >>> On 12.08.10 at 18:37, Tim Deegan wrote: > At 16:09 +0100 on 12 Aug (1281629364), Jan Beulich wrote: >> >>> On 23.07.10 at 15:49, Tim Deegan wrote: >> > There are a few places in Xen where we walk a domain's page lists >> > without holding the page_alloc lock. They race with updates to the = page >> > lists, which are normally rare but can be quite common under PoD when >> > the domain is close to its memory limit and the PoD reclaimer is = busy. >> > This patch protects those places by taking the page_alloc lock. >> >=20 >> > I think this is OK for the two debug-key printouts - they don't run = from >> > irq context and look deadlock-free. The tboot change seems safe too >>=20 >> While the comment says the patch would leave debug key printouts >> alone, ... >=20 > Sorry, my intention was to say that changes to the debug-key printouts > are safe, not that they didn't require changes. =20 >=20 > The debug-key printouts (in particular the NUMA one) are where I > actually hit this bug on a running system. But then, to avoid a hanging system, these should be trylock-s rather than plain locks, shouldn't they? Jan