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From: Zhang Yi <yi.zhang@huawei.com>
To: <linux-ext4@vger.kernel.org>
Cc: <linux-fsdevel@vger.kernel.org>, <tytso@mit.edu>,
	<adilger.kernel@dilger.ca>, <jack@suse.cz>, <yi.zhang@huawei.com>,
	<yukuai3@huawei.com>
Subject: [RFC PATCH v2 6/7] fs: introduce a usage count into the superblock
Date: Wed, 14 Apr 2021 21:47:36 +0800
Message-ID: <20210414134737.2366971-7-yi.zhang@huawei.com> (raw)
In-Reply-To: <20210414134737.2366971-1-yi.zhang@huawei.com>

Commit <87d8fe1ee6b8> ("add releasepage hooks to block devices which can
be used by file systems") introduce a hook that used by ext4 filesystem
to release journal buffers, but it doesn't add corresponding concurrency
protection that ->bdev_try_to_free_page() could be raced by umount
filesystem concurrently. This patch add a usage count on superblock that
filesystem can use it to prevent above race and make invoke
->bdev_try_to_free_page() safe.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 include/linux/fs.h | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index ec8f3ddf4a6a..3c6a5c08c2df 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -41,6 +41,7 @@
 #include <linux/stddef.h>
 #include <linux/mount.h>
 #include <linux/cred.h>
+#include <linux/percpu-refcount.h>
 
 #include <asm/byteorder.h>
 #include <uapi/linux/fs.h>
@@ -1547,6 +1548,13 @@ struct super_block {
 
 	spinlock_t		s_inode_wblist_lock;
 	struct list_head	s_inodes_wb;	/* writeback inodes */
+
+	/*
+	 * Count users who are using the super_block, used to protect
+	 * umount filesystem concurrently with others.
+	 */
+	struct percpu_ref	s_usage_counter;
+	wait_queue_head_t	s_usage_waitq;
 } __randomize_layout;
 
 /* Helper functions so that in most cases filesystems will
@@ -1765,6 +1773,27 @@ static inline bool sb_start_intwrite_trylock(struct super_block *sb)
 bool inode_owner_or_capable(struct user_namespace *mnt_userns,
 			    const struct inode *inode);
 
+static inline void sb_usage_counter_release(struct percpu_ref *ref)
+{
+	struct super_block *sb;
+
+	sb = container_of(ref, struct super_block, s_usage_counter);
+	wake_up(&sb->s_usage_waitq);
+}
+
+static inline int sb_usage_counter_init(struct super_block *sb)
+{
+	init_waitqueue_head(&sb->s_usage_waitq);
+	return percpu_ref_init(&sb->s_usage_counter, sb_usage_counter_release,
+			       0, GFP_KERNEL);
+}
+
+static inline void sb_usage_counter_wait(struct super_block *sb)
+{
+	percpu_ref_kill(&sb->s_usage_counter);
+	wait_event(sb->s_usage_waitq, percpu_ref_is_zero(&sb->s_usage_counter));
+}
+
 /*
  * VFS helper functions..
  */
-- 
2.25.4


  parent reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-14 13:47 [RFC PATCH v2 0/7] ext4, jbd2: fix 3 issues about bdev_try_to_free_page() Zhang Yi
2021-04-14 13:47 ` [RFC PATCH v2 1/7] jbd2: remove the out label in __jbd2_journal_remove_checkpoint() Zhang Yi
2021-04-21 10:01   ` Jan Kara
2021-04-14 13:47 ` [RFC PATCH v2 2/7] jbd2: ensure abort the journal if detect IO error when writing original buffer back Zhang Yi
2021-04-21 13:20   ` Jan Kara
2021-04-14 13:47 ` [RFC PATCH v2 3/7] jbd2: don't abort the journal when freeing buffers Zhang Yi
2021-04-21 13:23   ` Jan Kara
2021-04-14 13:47 ` [RFC PATCH v2 4/7] jbd2: do not free buffers in jbd2_journal_try_to_free_buffers() Zhang Yi
2021-04-15 14:46   ` Christoph Hellwig
2021-04-14 13:47 ` [RFC PATCH v2 5/7] ext4: use RCU to protect accessing superblock in blkdev_releasepage() Zhang Yi
2021-04-15 14:48   ` Christoph Hellwig
2021-04-14 13:47 ` Zhang Yi [this message]
2021-04-15 14:40   ` [RFC PATCH v2 6/7] fs: introduce a usage count into the superblock Christoph Hellwig
2021-04-16  8:00     ` Zhang Yi
2021-04-14 13:47 ` [RFC PATCH v2 7/7] ext4: fix race between blkdev_releasepage() and ext4_put_super() Zhang Yi
2021-04-15 14:52   ` Christoph Hellwig
2021-04-16  8:00     ` Zhang Yi
2021-04-20 13:08       ` Christoph Hellwig
2021-04-21 13:46         ` Jan Kara
2021-04-21 16:57           ` Theodore Ts'o
2021-04-22  9:04             ` Jan Kara
2021-04-23 11:39               ` Zhang Yi
2021-04-23 16:06                 ` Jan Kara
2021-04-23 14:40               ` Theodore Ts'o

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