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

[Chao Yu]

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 <cheny...@huawei.com>
Signed-off-by: Chao Yu <yuch...@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