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From: Christoph Hellwig <hch@lst.de>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>,
	Qian Cai <quic_qiancai@quicinc.com>, Jens Axboe <axboe@kernel.dk>,
	Tejun Heo <tj@kernel.org>,
	linux-block@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	cgroups@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: move the bdi from the request_queue to the gendisk
Date: Wed, 11 Aug 2021 13:51:47 +0200	[thread overview]
Message-ID: <20210811115147.GA27860@lst.de> (raw)
In-Reply-To: <20210811112514.GC14725@quack2.suse.cz>

On Wed, Aug 11, 2021 at 01:25:14PM +0200, Jan Kara wrote:
> Well, non-default bdi_writeback structures do hold bdi reference - see
> wb_exit() which drops the reference. I think the problem rather was that a
> block device's inode->i_wb was pointing to the default bdi_writeback
> structure and that got freed after bdi_put() before block device inode was
> shutdown through bdput()... So what I think we need is that if the inode
> references the default writeback structure, it actually holds a reference
> to the bdi.

Qian, can you test the patch below instead of the one I sent yesterday?

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index cd06dca232c3..edfb7ce2cc93 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -283,8 +283,7 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 
 	memset(wb, 0, sizeof(*wb));
 
-	if (wb != &bdi->wb)
-		bdi_get(bdi);
+	bdi_get(bdi);
 	wb->bdi = bdi;
 	wb->last_old_flush = jiffies;
 	INIT_LIST_HEAD(&wb->b_dirty);
@@ -362,8 +361,7 @@ static void wb_exit(struct bdi_writeback *wb)
 		percpu_counter_destroy(&wb->stat[i]);
 
 	fprop_local_destroy_percpu(&wb->completions);
-	if (wb != &wb->bdi->wb)
-		bdi_put(wb->bdi);
+	bdi_put(wb->bdi);
 }
 
 #ifdef CONFIG_CGROUP_WRITEBACK

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
To: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
Cc: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>,
	Qian Cai <quic_qiancai-jfJNa2p1gH1BDgjK7y7TUQ@public.gmane.org>,
	Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>,
	Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org
Subject: Re: move the bdi from the request_queue to the gendisk
Date: Wed, 11 Aug 2021 13:51:47 +0200	[thread overview]
Message-ID: <20210811115147.GA27860@lst.de> (raw)
In-Reply-To: <20210811112514.GC14725-4I4JzKEfoa/jFM9bn6wA6Q@public.gmane.org>

On Wed, Aug 11, 2021 at 01:25:14PM +0200, Jan Kara wrote:
> Well, non-default bdi_writeback structures do hold bdi reference - see
> wb_exit() which drops the reference. I think the problem rather was that a
> block device's inode->i_wb was pointing to the default bdi_writeback
> structure and that got freed after bdi_put() before block device inode was
> shutdown through bdput()... So what I think we need is that if the inode
> references the default writeback structure, it actually holds a reference
> to the bdi.

Qian, can you test the patch below instead of the one I sent yesterday?

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index cd06dca232c3..edfb7ce2cc93 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -283,8 +283,7 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 
 	memset(wb, 0, sizeof(*wb));
 
-	if (wb != &bdi->wb)
-		bdi_get(bdi);
+	bdi_get(bdi);
 	wb->bdi = bdi;
 	wb->last_old_flush = jiffies;
 	INIT_LIST_HEAD(&wb->b_dirty);
@@ -362,8 +361,7 @@ static void wb_exit(struct bdi_writeback *wb)
 		percpu_counter_destroy(&wb->stat[i]);
 
 	fprop_local_destroy_percpu(&wb->completions);
-	if (wb != &wb->bdi->wb)
-		bdi_put(wb->bdi);
+	bdi_put(wb->bdi);
 }
 
 #ifdef CONFIG_CGROUP_WRITEBACK

  reply	other threads:[~2021-08-11 11:51 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09 14:17 move the bdi from the request_queue to the gendisk Christoph Hellwig
2021-08-09 14:17 ` [PATCH 1/5] mm: hide laptop_mode_wb_timer entirely behind the BDI API Christoph Hellwig
2021-08-09 14:17   ` Christoph Hellwig
2021-08-09 14:33   ` Johannes Thumshirn
2021-08-09 14:33     ` Johannes Thumshirn
2021-08-09 15:10   ` Jan Kara
2021-08-09 15:10     ` Jan Kara
2021-08-10 21:56   ` Guenter Roeck
2021-08-10 21:56     ` Guenter Roeck
2021-08-11  5:22     ` Christoph Hellwig
2021-08-11  5:22       ` Christoph Hellwig
2021-08-09 14:17 ` [PATCH 2/5] block: pass a gendisk to blk_queue_update_readahead Christoph Hellwig
2021-08-09 14:17   ` Christoph Hellwig
2021-08-09 14:35   ` Johannes Thumshirn
2021-08-09 15:17   ` Jan Kara
2021-08-09 14:17 ` [PATCH 3/5] block: add a queue_has_disk helper Christoph Hellwig
2021-08-09 14:17   ` Christoph Hellwig
2021-08-09 14:37   ` Johannes Thumshirn
2021-08-09 15:18   ` Jan Kara
2021-08-09 14:17 ` [PATCH 4/5] block: move the bdi from the request_queue to the gendisk Christoph Hellwig
2021-08-09 14:38   ` Johannes Thumshirn
2021-08-09 14:38     ` Johannes Thumshirn
2021-08-09 15:47   ` Jan Kara
2021-08-09 17:57     ` Jens Axboe
2021-08-09 17:57       ` Jens Axboe
2021-08-09 21:29       ` Jan Kara
2021-08-10 16:44     ` Christoph Hellwig
2021-10-14 14:31   ` [sparc64] kernel OOPS (was: [PATCH 4/5] block: move the bdi from the request_queue to the gendisk) Anatoly Pugachev
2021-10-14 14:32     ` Christoph Hellwig
2021-10-14 14:32       ` Christoph Hellwig
2021-10-14 20:27       ` Anatoly Pugachev
2021-08-09 14:17 ` [PATCH 5/5] block: remove the bd_bdi in struct block_device Christoph Hellwig
2021-08-09 14:17   ` Christoph Hellwig
2021-08-09 14:55   ` Johannes Thumshirn
2021-08-09 15:49   ` Jan Kara
2021-08-09 21:42 ` move the bdi from the request_queue to the gendisk Jens Axboe
2021-08-09 21:42   ` Jens Axboe
2021-08-10 19:36 ` Qian Cai
2021-08-10 19:36   ` Qian Cai
2021-08-10 20:02   ` Christoph Hellwig
2021-08-10 20:02     ` Christoph Hellwig
2021-08-11  2:28     ` Qian Cai
2021-08-11  2:28       ` Qian Cai
2021-08-11 11:25     ` Jan Kara
2021-08-11 11:51       ` Christoph Hellwig [this message]
2021-08-11 11:51         ` Christoph Hellwig
2021-08-11 12:47         ` Jan Kara

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