f2fs: avoid deadlock during evict after f2fs_gc

o Deadlock case #1

Thread 1:
- writeback_sb_inodes
 - do_writepages
  - f2fs_write_data_pages
   - write_cache_pages
    - f2fs_write_data_page
     - f2fs_balance_fs
      - wait mutex_lock(gc_mutex)

Thread 2:
- f2fs_balance_fs
 - mutex_lock(gc_mutex)
 - f2fs_gc
  - f2fs_iget
   - wait iget_locked(inode->i_lock)

Thread 3:
- do_unlinkat
 - iput
  - lock(inode->i_lock)
   - evict
    - inode_wait_for_writeback

o Deadlock case #2

Thread 1:
- __writeback_single_inode
 : set I_SYNC
  - do_writepages
   - f2fs_write_data_page
    - f2fs_balance_fs
     - f2fs_gc
      - iput
       - evict
        - inode_wait_for_writeback(I_SYNC)

In order to avoid this, even though iput is called with the zero-reference
count, we need to stop the eviction procedure if the inode is on writeback.
So this patch links f2fs_drop_inode which checks the I_SYNC flag.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 2db9380f5dda..61b44542417c 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -577,6 +577,7 @@ static int f2fs_write_data_pages(struct address_space *mapping,
 {
 	struct inode *inode = mapping->host;
 	struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);
+	bool locked = false;
 	int ret;
 	long excess_nrtw = 0, desired_nrtw;
 
@@ -590,10 +591,12 @@ static int f2fs_write_data_pages(struct address_space *mapping,
 		wbc->nr_to_write = desired_nrtw;
 	}
 
-	if (!S_ISDIR(inode->i_mode))
+	if (!S_ISDIR(inode->i_mode)) {
 		mutex_lock(&sbi->writepages);
+		locked = true;
+	}
 	ret = write_cache_pages(mapping, wbc, __f2fs_writepage, mapping);
-	if (!S_ISDIR(inode->i_mode))
+	if (locked)
 		mutex_unlock(&sbi->writepages);
 	f2fs_submit_bio(sbi, DATA, (wbc->sync_mode == WB_SYNC_ALL));