196 lines
8.1 KiB
Diff
196 lines
8.1 KiB
Diff
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Path: news.gmane.org!not-for-mail
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From: ebiederm@xmission.com (Eric W. Biederman)
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Newsgroups: gmane.linux.kernel
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Subject: Re: Odd ENOMEM being returned in 3.8-rcX
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Date: Fri, 08 Feb 2013 12:13:09 -0800
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Lines: 117
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Approved: news@gmane.org
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Message-ID: <87k3qiwomi.fsf@xmission.com>
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References: <20130207215742.GB31684@hansolo.jdub.homelinux.org>
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<20130207141502.04625ea0.akpm@linux-foundation.org>
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<20130208003501.GC31684@hansolo.jdub.homelinux.org>
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<20130208181949.GD31684@hansolo.jdub.homelinux.org>
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X-Trace: ger.gmane.org 1360354410 32723 80.91.229.3 (8 Feb 2013 20:13:30 GMT)
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NNTP-Posting-Date: Fri, 8 Feb 2013 20:13:30 +0000 (UTC)
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Cc: Andrew Morton <akpm@linux-foundation.org>,
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Al Viro <viro@zeniv.linux.org.uk>,
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Mel Gorman <mgorman@suse.de>, linux-kernel@vger.kernel.org
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To: Josh Boyer <jwboyer@redhat.com>
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Original-X-From: linux-kernel-owner@vger.kernel.org Fri Feb 08 21:13:50 2013
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for glk-linux-kernel-3@plane.gmane.org; Fri, 08 Feb 2013 21:13:49 +0100
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In-Reply-To: <20130208181949.GD31684@hansolo.jdub.homelinux.org> (Josh Boyer's
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message of "Fri, 8 Feb 2013 13:19:49 -0500")
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List-ID: <linux-kernel.vger.kernel.org>
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X-Mailing-List: linux-kernel@vger.kernel.org
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Xref: news.gmane.org gmane.linux.kernel:1438656
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Archived-At: <http://permalink.gmane.org/gmane.linux.kernel/1438656>
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Josh Boyer <jwboyer@redhat.com> writes:
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> On Thu, Feb 07, 2013 at 07:35:01PM -0500, Josh Boyer wrote:
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>> On Thu, Feb 07, 2013 at 02:15:02PM -0800, Andrew Morton wrote:
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>> > On Thu, 7 Feb 2013 16:57:42 -0500
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>> > Josh Boyer <jwboyer@redhat.com> wrote:
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>> >
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>> > > Hi All,
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>> > >
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>> > > We've hit a weird error in Fedora using the 3.8-rcX kernels. It seems
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>> > > the mock tool is getting back ENOMEM when doing very simple things that
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>> > > normally just work. The 3.7 kernels on the same userspace work just
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>> > > fine. It seems just running 'mock init -v' is enough to cause the
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>> > > failure.
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>> >
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>> > I assume you're not seeing the "page allocation failure" message and
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>> > backtrace. This means that either
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>>
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>> Right. If I disable our debug options, I see no backtraces at all and
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>> the python app still gets ENOMEM returned. (See below for those
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>> interested).
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>>
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>> > a) it's a __GFP_NOWARN callsite. This is rare. Or
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>> >
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>> > b) it's actually a different error but someone went and overwrote a
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>> > callee's return value with -ENOMEM. We do this a lot and it sucks.
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>>
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>> We do it in copy_io :\.
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>>
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>> > > At first glance it seems copy_io is failing (possibly because
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>> > > get_task_io_context fails), and then the above fallout is printed. The
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>> > > warning seems fairly valid, but I don't think that is the root of the
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>> > > problem.
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>> >
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>> > yes, get_task_io_context() might be the place. Tried adding a few
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>> > error-path printks in there to see what's happening?
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>>
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>> Yeah, that's my next step. I guess I know what I'll be doing tomorrow.
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>>
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>> > I can't see anything around there which leaves interrupts disabled
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>> > though. It's quite likely that there's some code with is forgetting to
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>> > reenable interrupts on a rarely-tested error path, and that ENOMEM is
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>> > tickling the bug.
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>>
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>> Right, agreed. As I said, I think that is mostly a secondary issue.
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>> Hopefully it will be easy to fix once we figure out why we're getting
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>> the ENOMEM error.
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>>
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>> Python backtrace below. Seems to be failing on forking a umount command
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>> after init'ing the chroot. I can put the full output somewhere if
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>> people are interested.
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>
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> OK. I've bisected this down to:
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>
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> 50804fe3737ca6a5942fdc2057a18a8141d00141 is the first bad commit
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> commit 50804fe3737ca6a5942fdc2057a18a8141d00141
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> Author: Eric W. Biederman <ebiederm@xmission.com>
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> Date: Tue Mar 2 15:41:50 2010 -0800
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>
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> pidns: Support unsharing the pid namespace.
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>
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>
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> I haven't really gotten much farther than that yet, but the bisect was
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> pretty straight forward. Eric, is there anything specific I can gather
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> or do to help figure out why that is causing mock to get such a weird
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> error? I can provide the bisect log if you'd like.
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My best guess in some dark corner of mock has untested code to unshare a
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pid namespace, and that corner started doing something now that
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unsharing of the pid namespace actually works.
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If mock has called unshare(CLONE_NEWPID). And then forked a process and
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that process exited, and then forked anothe process that second and all
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subsequent fork calls will fail with -ENOMEM (because init has exited in
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the pid namespace). -ENOMEM will be generated because of a failure of
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alloc_pid.
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Looking at that code path a little closer that just about has to be it,
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because I goofed and the error path drops the lock but not irqs. The
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patch below should fix the nasty warning and confirm where the code is
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failing in copy_process.
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An strace to see which syscalls mock is making and with which flags
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would be very interesting. I am almost certain that there is a
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unshare(CLONE_NEWPID) somewhere in there. But in a remote corner of
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possibility it could weird clone flags, or something else.
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Beyond that I suspect we want to work with the mock folks so they get
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their code to use a pid namespace working the way they intended.
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Eric
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From: "Eric W. Biederman" <ebiederm@xmission.com>
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Date: Fri, 8 Feb 2013 12:05:54 -0800
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Subject: [PATCH] pid: unlock_irq when alloc_pid fails because init has
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exited.
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Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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---
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kernel/pid.c | 2 +-
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1 files changed, 1 insertions(+), 1 deletions(-)
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diff --git a/kernel/pid.c b/kernel/pid.c
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index de9af60..f2c6a68 100644
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--- a/kernel/pid.c
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+++ b/kernel/pid.c
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@@ -331,7 +331,7 @@ out:
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return pid;
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out_unlock:
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- spin_unlock(&pidmap_lock);
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+ spin_unlock_irq(&pidmap_lock);
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out_free:
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while (++i <= ns->level)
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free_pidmap(pid->numbers + i);
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--
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1.7.5.4
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