[PATCH v3] f2fs: fix to keep isolation of atomic write

Chao Yu
2021-04-12T08:15:59Z

As Yi Chen reported, there is a potential race case described as below:

Thread A Thread B
- f2fs_ioc_start_atomic_write
- mkwrite
- set_page_dirty
- f2fs_set_page_private(page, 0)
- set_inode_flag(FI_ATOMIC_FILE)
- mkwrite same page
- set_page_dirty
- f2fs_register_inmem_page
- f2fs_set_page_private(ATOMIC_WRITTEN_PAGE)
failed due to PagePrivate flag has been set
- list_add_tail
- truncate_inode_pages
- f2fs_invalidate_page
- clear page private but w/o remove it from
inmem_list
- set page->mapping to NULL
- f2fs_ioc_commit_atomic_write
- __f2fs_commit_inmem_pages
- __revoke_inmem_pages
- f2fs_put_page panic as page->mapping is NULL

The root cause is we missed to keep isolation of atomic write in the case
of start_atomic_write vs mkwrite, let start_atomic_write helds i_mmap_sem
lock to avoid this issue.

Reported-by: Yi Chen <chenyi77@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
v3:
- rebase to last dev branch
- update commit message because this patch fixes a different racing issue
of atomic write
fs/f2fs/file.c | 3 +++
fs/f2fs/segment.c | 6 ++++++
2 files changed, 9 insertions(+)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index d697c8900fa7..6284b2f4a60b 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2054,6 +2054,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
goto out;

down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
+ down_write(&F2FS_I(inode)->i_mmap_sem);

/*
* Should wait end_io to count F2FS_WB_CP_DATA correctly by
@@ -2064,6 +2065,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
inode->i_ino, get_dirty_pages(inode));
ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
if (ret) {
+ up_write(&F2FS_I(inode)->i_mmap_sem);
up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
goto out;
}
@@ -2077,6 +2079,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
/* add inode in inmem_list first and set atomic_file */
set_inode_flag(inode, FI_ATOMIC_FILE);
clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
+ up_write(&F2FS_I(inode)->i_mmap_sem);
up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);

f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 0cb1ca88d4aa..78c8342f52fd 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -325,6 +325,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
struct f2fs_inode_info *fi = F2FS_I(inode);

do {
+ down_write(&F2FS_I(inode)->i_mmap_sem);
mutex_lock(&fi->inmem_lock);
if (list_empty(&fi->inmem_pages)) {
fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
@@ -339,11 +340,13 @@ void f2fs_drop_inmem_pages(struct inode *inode)
spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);

mutex_unlock(&fi->inmem_lock);
+ up_write(&F2FS_I(inode)->i_mmap_sem);
break;
}
__revoke_inmem_pages(inode, &fi->inmem_pages,
true, false, true);
mutex_unlock(&fi->inmem_lock);
+ up_write(&F2FS_I(inode)->i_mmap_sem);
} while (1);
}

@@ -468,6 +471,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
f2fs_balance_fs(sbi, true);

down_write(&fi->i_gc_rwsem[WRITE]);
+ down_write(&F2FS_I(inode)->i_mmap_sem);

f2fs_lock_op(sbi);
set_inode_flag(inode, FI_ATOMIC_COMMIT);
@@ -479,6 +483,8 @@ int f2fs_commit_inmem_pages(struct inode *inode)
clear_inode_flag(inode, FI_ATOMIC_COMMIT);

f2fs_unlock_op(sbi);
+
+ up_write(&F2FS_I(inode)->i_mmap_sem);
up_write(&fi->i_gc_rwsem[WRITE]);

return err;
--
2.29.2