linux-kernel - Re: [PATCH 7/9] x86/pci: Pass lockdep condition to pcm_mmcfg

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Message-ID: <20190716040303.GA73383@google.com>
Date:   Tue, 16 Jul 2019 00:03:03 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Borislav Petkov <bp@...en8.de>, c0d1n61at3@...il.com,
        "David S. Miller" <davem@...emloft.net>, edumazet@...gle.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Josh Triplett <josh@...htriplett.org>, keescook@...omium.org,
        kernel-hardening@...ts.openwall.com, kernel-team@...roid.com,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        neilb@...e.com, netdev@...r.kernel.org,
        Oleg Nesterov <oleg@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Pavel Machek <pavel@....cz>, peterz@...radead.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        rcu@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Tejun Heo <tj@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, will@...nel.org,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH 7/9] x86/pci: Pass lockdep condition to pcm_mmcfg_list
 iterator (v1)

On Mon, Jul 15, 2019 at 03:02:35PM -0500, Bjorn Helgaas wrote:
> On Mon, Jul 15, 2019 at 10:37:03AM -0400, Joel Fernandes (Google) wrote:
> > The pcm_mmcfg_list is traversed with list_for_each_entry_rcu without a
> > reader-lock held, because the pci_mmcfg_lock is already held. Make this
> > known to the list macro so that it fixes new lockdep warnings that
> > trigger due to lockdep checks added to list_for_each_entry_rcu().
> > 
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> 
> Ingo takes care of most patches to this file, but FWIW,
> 
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

Thanks.

> I would personally prefer if you capitalized the subject to match the
> "x86/PCI:" convention that's used fairly consistently in
> arch/x86/pci/.
> 
> Also, I didn't apply this to be sure, but it looks like this might
> make a line or two wider than 80 columns, which I would rewrap if I
> were applying this.

Updated below is the patch with the nits corrected:

---8<-----------------------

>From 73fab09d7e33ca2110c24215f8ed428c12625dbe Mon Sep 17 00:00:00 2001
From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
Date: Sat, 1 Jun 2019 15:05:49 -0400
Subject: [PATCH] x86/PCI: Pass lockdep condition to pcm_mmcfg_list iterator
 (v1)

The pcm_mmcfg_list is traversed with list_for_each_entry_rcu without a
reader-lock held, because the pci_mmcfg_lock is already held. Make this
known to the list macro so that it fixes new lockdep warnings that
trigger due to lockdep checks added to list_for_each_entry_rcu().

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 arch/x86/pci/mmconfig-shared.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/pci/mmconfig-shared.c b/arch/x86/pci/mmconfig-shared.c
index 7389db538c30..9e3250ec5a37 100644
--- a/arch/x86/pci/mmconfig-shared.c
+++ b/arch/x86/pci/mmconfig-shared.c
@@ -29,6 +29,7 @@
 static bool pci_mmcfg_running_state;
 static bool pci_mmcfg_arch_init_failed;
 static DEFINE_MUTEX(pci_mmcfg_lock);
+#define pci_mmcfg_lock_held() lock_is_held(&(pci_mmcfg_lock).dep_map)
 
 LIST_HEAD(pci_mmcfg_list);
 
@@ -54,7 +55,8 @@ static void list_add_sorted(struct pci_mmcfg_region *new)
 	struct pci_mmcfg_region *cfg;
 
 	/* keep list sorted by segment and starting bus number */
-	list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list) {
+	list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list,
+				pci_mmcfg_lock_held()) {
 		if (cfg->segment > new->segment ||
 		    (cfg->segment == new->segment &&
 		     cfg->start_bus >= new->start_bus)) {
@@ -118,7 +120,8 @@ struct pci_mmcfg_region *pci_mmconfig_lookup(int segment, int bus)
 {
 	struct pci_mmcfg_region *cfg;
 
-	list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list)
+	list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list
+				pci_mmcfg_lock_held())
 		if (cfg->segment == segment &&
 		    cfg->start_bus <= bus && bus <= cfg->end_bus)
 			return cfg;
-- 
2.22.0.510.g264f2c817a-goog