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Subject[PATCH 4.18 088/197] f2fs: avoid race between zero_range and background GC
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chao Yu <yuchao0@huawei.com>

[ Upstream commit c7079853c859c910b9d047a37891b4aafb8f8dd7 ]

Thread A Background GC
- f2fs_zero_range
- truncate_pagecache_range
- gc_data_segment
- get_read_data_page
- move_data_page
- set_page_dirty
- set_cold_data
- f2fs_do_zero_range
- dn->data_blkaddr = NEW_ADDR;
- f2fs_set_data_blkaddr

Actually, we don't need to set dirty & checked flag on the page, since
all valid data in the page should be zeroed by zero_range().

Use i_gc_rwsem[WRITE] to avoid such race condition.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/f2fs/file.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1295,8 +1295,6 @@ static int f2fs_zero_range(struct inode
if (ret)
goto out_sem;

- truncate_pagecache_range(inode, offset, offset + len - 1);
-
pg_start = ((unsigned long long) offset) >> PAGE_SHIFT;
pg_end = ((unsigned long long) offset + len) >> PAGE_SHIFT;

@@ -1326,12 +1324,19 @@ static int f2fs_zero_range(struct inode
unsigned int end_offset;
pgoff_t end;

+ down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
+
+ truncate_pagecache_range(inode,
+ (loff_t)index << PAGE_SHIFT,
+ ((loff_t)pg_end << PAGE_SHIFT) - 1);
+
f2fs_lock_op(sbi);

set_new_dnode(&dn, inode, NULL, NULL, 0);
ret = f2fs_get_dnode_of_data(&dn, index, ALLOC_NODE);
if (ret) {
f2fs_unlock_op(sbi);
+ up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
goto out;
}

@@ -1340,7 +1345,9 @@ static int f2fs_zero_range(struct inode

ret = f2fs_do_zero_range(&dn, index, end);
f2fs_put_dnode(&dn);
+
f2fs_unlock_op(sbi);
+ up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);

f2fs_balance_fs(sbi, dn.node_changed);


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