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Date:   Wed, 15 Jun 2022 15:38:45 +0200
From:   Jan Kara <jack@suse.cz>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Thomas Backlund <tmb@tmb.nu>, Jan Kara <jack@suse.cz>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>, patches@kernelci.org,
        lkft-triage@lists.linaro.org, Pavel Machek <pavel@denx.de>,
        Jon Hunter <jonathanh@nvidia.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
        Slade Watkins <slade@sladewatkins.com>
Subject: Re: [PATCH 5.15 000/251] 5.15.47-rc2 review
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On Wed 15-06-22 13:00:22, Jan Kara wrote:
> On Tue 14-06-22 12:00:22, Linus Torvalds wrote:
> > On Tue, Jun 14, 2022 at 11:51 AM Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > Or just make sure that noop_backing_dev_info is fully initialized
> > > before it's used.
> > 
> > I don't see any real reason why that
> > 
> >     err = bdi_init(&noop_backing_dev_info);
> > 
> > couldn't just be done very early. Maybe as the first call in
> > driver_init(), before the whole devtmpfs_init() etc.
> 
> I've checked the dependencies and cgroups (which are the only non-trivial
> dependency besides per-CPU infrastructure) are initialized early enough so
> it should work fine. So let's try that.

Attached patch boots for me. Guys, who was able to reproduce the failure: Can
you please confirm this patch fixes your problem?

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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	filename="0001-init-Initialized-noop_backing_dev_info-early.patch"

From 8f998b182be7563fc92aa8914cc7d21f75a3c20e Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Wed, 15 Jun 2022 15:22:29 +0200
Subject: [PATCH] init: Initialized noop_backing_dev_info early

noop_backing_dev_info is used by superblocks of various
pseudofilesystems such as kdevtmpfs. Initialize it before the
filesystems get mounted.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 drivers/base/init.c         |  2 ++
 include/linux/backing-dev.h |  2 ++
 mm/backing-dev.c            | 11 ++---------
 3 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/base/init.c b/drivers/base/init.c
index d8d0fe687111..397eb9880cec 100644
--- a/drivers/base/init.c
+++ b/drivers/base/init.c
@@ -8,6 +8,7 @@
 #include <linux/init.h>
 #include <linux/memory.h>
 #include <linux/of.h>
+#include <linux/backing-dev.h>
 
 #include "base.h"
 
@@ -20,6 +21,7 @@
 void __init driver_init(void)
 {
 	/* These are the core pieces */
+	bdi_init(&noop_backing_dev_info);
 	devtmpfs_init();
 	devices_init();
 	buses_init();
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 2bd073fa6bb5..f0baef68f90f 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -119,6 +119,8 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
 
 extern struct backing_dev_info noop_backing_dev_info;
 
+extern int bdi_init(struct backing_dev_info *bdi);
+
 /**
  * writeback_in_progress - determine whether there is writeback in progress
  * @wb: bdi_writeback of interest
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index ff60bd7d74e0..95550b8fa7fe 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -231,20 +231,13 @@ static __init int bdi_class_init(void)
 }
 postcore_initcall(bdi_class_init);
 
-static int bdi_init(struct backing_dev_info *bdi);
-
 static int __init default_bdi_init(void)
 {
-	int err;
-
 	bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_UNBOUND |
 				 WQ_SYSFS, 0);
 	if (!bdi_wq)
 		return -ENOMEM;
-
-	err = bdi_init(&noop_backing_dev_info);
-
-	return err;
+	return 0;
 }
 subsys_initcall(default_bdi_init);
 
@@ -781,7 +774,7 @@ static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
 
 #endif	/* CONFIG_CGROUP_WRITEBACK */
 
-static int bdi_init(struct backing_dev_info *bdi)
+int bdi_init(struct backing_dev_info *bdi)
 {
 	int ret;
 
-- 
2.35.3


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