Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755166AbdDLTl2 (ORCPT ); Wed, 12 Apr 2017 15:41:28 -0400 Received: from mail-qt0-f193.google.com ([209.85.216.193]:36463 "EHLO mail-qt0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753929AbdDLTlY (ORCPT ); Wed, 12 Apr 2017 15:41:24 -0400 Subject: Re: WARN @lib/refcount.c:128 during hot unplug of I/O adapter. To: Michael Ellerman , Tyrel Datwyler , Sachin Sant , linuxppc-dev@ozlabs.org References: <8760ig983f.fsf@concordia.ellerman.id.au> <89aec36c-e352-e055-5e80-1235449762ce@linux.vnet.ibm.com> <871sszwc87.fsf@concordia.ellerman.id.au> <87efwyv0j7.fsf@concordia.ellerman.id.au> Cc: Nathan Fontenot , LKML From: Tyrel Datwyler Message-ID: Date: Wed, 12 Apr 2017 12:41:20 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <87efwyv0j7.fsf@concordia.ellerman.id.au> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4608 Lines: 144 On 04/11/2017 07:10 PM, Michael Ellerman wrote: > Tyrel Datwyler writes: >> On 04/11/2017 02:00 AM, Michael Ellerman wrote: >>> Tyrel Datwyler writes: >>>> I started looking at it when Bharata submitted a patch trying to fix the >>>> issue for CPUs, but got side tracked by other things. I suspect that >>>> this underflow has actually been an issue for quite some time, and we >>>> are just now becoming aware of it thanks to the recount_t patchset being >>>> merged. >>> >>> Yes I agree. Which means it might be broken in existing distros. >> >> Definitely. I did some profiling last night, and I understand the >> hotplug case. It turns out to be as I suggested in the original thread >> about CPUs. When the devicetree code was worked to move the tree out of >> proc and into sysfs the sysfs detach code added a of_node_put to remove >> the original of_init reference. pSeries Being the sole original >> *dynamic* device tree user we had always issued a of_node_put in our >> dlpar specific detach function to achieve that end. So, this should be a >> pretty straight forward trivial fix. > > Excellent, thanks. > >> However, for the case where devices are present at boot it appears we a >> leaking a lot of references resulting in the device nodes never actually >> being released/freed after a dlpar remove. In the CPU case after boot I >> count 8 more references taken than the hotplug case, and corresponding >> of_node_put's are not called at dlpar remove time either. That will take >> some time to track them down, review and clean up. I found our reference leak. In topology_init() we call register_cpu() for each possible logical cpu id. For any logical cpu present a reference to the device node of the cpu core is grabbed and added to cpu->dev.of_node. Which matches what I'm seeing on a Power8 lpar, 8 extraneous references which is equal to the 8 hardware threads of a core. > > Yes that is a perennial problem unfortunately which we've never come up > with a good solution for. > > The (old) patch below might help track some of them down. I remember > having a script to process the output of the trace and find mismatches, > but I can't find it right now - but I'm sure you can hack up something > :) Haha, this patch is almost identical to what I hacked up Monday to get an idea of where the refcounts were at. Probably wouldn't hurt to try and upstream it into the driver/of tree. -Tyrel > > cheers > > > diff --git a/arch/powerpc/include/asm/trace.h b/arch/powerpc/include/asm/trace.h > index 32e36b16773f..ad32365082a0 100644 > --- a/arch/powerpc/include/asm/trace.h > +++ b/arch/powerpc/include/asm/trace.h > @@ -168,6 +168,44 @@ TRACE_EVENT(hash_fault, > __entry->addr, __entry->access, __entry->trap) > ); > > +TRACE_EVENT(of_node_get, > + > + TP_PROTO(struct device_node *dn, int val), > + > + TP_ARGS(dn, val), > + > + TP_STRUCT__entry( > + __field(struct device_node *, dn) > + __field(int, val) > + ), > + > + TP_fast_assign( > + __entry->dn = dn; > + __entry->val = val; > + ), > + > + TP_printk("get %d -> %d %s", __entry->val - 1, __entry->val, __entry->dn->full_name) > +); > + > +TRACE_EVENT(of_node_put, > + > + TP_PROTO(struct device_node *dn, int val), > + > + TP_ARGS(dn, val), > + > + TP_STRUCT__entry( > + __field(struct device_node *, dn) > + __field(int, val) > + ), > + > + TP_fast_assign( > + __entry->dn = dn; > + __entry->val = val; > + ), > + > + TP_printk("put %d -> %d %s", __entry->val + 1, __entry->val, __entry->dn->full_name) > +); > + > #endif /* _TRACE_POWERPC_H */ > > #undef TRACE_INCLUDE_PATH > diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c > index c647bd1b6903..f5c3d761f3cd 100644 > --- a/drivers/of/dynamic.c > +++ b/drivers/of/dynamic.c > @@ -14,6 +14,8 @@ > > #include "of_private.h" > > +#include > + > /** > * of_node_get() - Increment refcount of a node > * @node: Node to inc refcount, NULL is supported to simplify writing of > @@ -23,8 +25,12 @@ > */ > struct device_node *of_node_get(struct device_node *node) > { > - if (node) > + if (node) { > kobject_get(&node->kobj); > + > + trace_of_node_get(node, atomic_read(&node->kobj.kref.refcount)); > + } > + > return node; > } > EXPORT_SYMBOL(of_node_get); > @@ -36,8 +42,10 @@ EXPORT_SYMBOL(of_node_get); > */ > void of_node_put(struct device_node *node) > { > - if (node) > + if (node) { > kobject_put(&node->kobj); > + trace_of_node_put(node, atomic_read(&node->kobj.kref.refcount)); > + } > } > EXPORT_SYMBOL(of_node_put); > >