linux-kernel - [PATCH] f2fs: remove race condition in releasing cblocks

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Message-Id: <20200508042506.143395-1-daeho43@gmail.com>
Date:   Fri,  8 May 2020 13:25:06 +0900
From:   Daeho Jeong <daeho43@...il.com>
To:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com
Cc:     Daeho Jeong <daehojeong@...gle.com>
Subject: [PATCH] f2fs: remove race condition in releasing cblocks

From: Daeho Jeong <daehojeong@...gle.com>

Now, if writing pages and releasing compress blocks occur
simultaneously, and releasing cblocks is executed more than one time
to a file, then total block count of filesystem and block count of the
file could be incorrect and damaged.

We have to execute releasing compress blocks only one time for a file
without being interfered by writepages path.

Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
---
 fs/f2fs/file.c | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 4aab4b42d8ba..a92bc51b9b28 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -3488,6 +3488,7 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)
 	pgoff_t page_idx = 0, last_idx;
 	unsigned int released_blocks = 0;
 	int ret;
+	int writecount;
 
 	if (!f2fs_sb_has_compression(F2FS_I_SB(inode)))
 		return -EOPNOTSUPP;
@@ -3509,13 +3510,29 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)
 
 	inode_lock(inode);
 
-	if (!IS_IMMUTABLE(inode)) {
-		F2FS_I(inode)->i_flags |= F2FS_IMMUTABLE_FL;
-		f2fs_set_inode_flags(inode);
-		inode->i_ctime = current_time(inode);
-		f2fs_mark_inode_dirty_sync(inode, true);
+	writecount = atomic_read(&inode->i_writecount);
+	if ((filp->f_mode & FMODE_WRITE && writecount != 1) || writecount) {
+		ret = -EBUSY;
+		goto out;
 	}
 
+	if (IS_IMMUTABLE(inode)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
+	if (ret)
+		goto out;
+
+	if (!F2FS_I(inode)->i_compr_blocks)
+		goto out;
+
+	F2FS_I(inode)->i_flags |= F2FS_IMMUTABLE_FL;
+	f2fs_set_inode_flags(inode);
+	inode->i_ctime = current_time(inode);
+	f2fs_mark_inode_dirty_sync(inode, true);
+
 	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 	down_write(&F2FS_I(inode)->i_mmap_sem);
 
@@ -3554,9 +3571,9 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)
 
 	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 	up_write(&F2FS_I(inode)->i_mmap_sem);
-
-	inode_unlock(inode);
 out:
+	inode_unlock(inode);
+
 	mnt_drop_write_file(filp);
 
 	if (ret >= 0) {
-- 
2.26.2.526.g744177e7f7-goog