f2fs: avoid RECLAIM_FS-ON-W: deadlock

This patch tries to avoid the following deadlock condition of which the reclaim
path can trigger f2fs_balance_fs again.

=================================
[ INFO: inconsistent lock state ]
---------------------------------
inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
kswapd0/41 [HC0[0]:SC0[0]:HE1:SE1] takes:
 (&sbi->gc_mutex){+.+.?.}, at: f2fs_balance_fs+0xe6/0x100 [f2fs]
{RECLAIM_FS-ON-W} state was registered at:
  [<ffffffff810aa5a9>] mark_held_locks+0xb9/0x140
  [<ffffffff810aae85>] lockdep_trace_alloc+0x85/0xf0
  [<ffffffff8113ab2c>] __alloc_pages_nodemask+0x7c/0x9b0
  [<ffffffff81175aa8>] alloc_pages_current+0xb8/0x180
  [<ffffffff811319cf>] __page_cache_alloc+0xaf/0xd0
  [<ffffffff8113225c>] find_or_create_page+0x4c/0xb0
  [<ffffffffa021359e>] find_data_page+0x14e/0x210 [f2fs]
  [<ffffffffa021161b>] f2fs_gc+0x9eb/0xd90 [f2fs]
  [<ffffffffa0218fae>] f2fs_balance_fs+0xee/0x100 [f2fs]
  [<ffffffffa020848c>] f2fs_setattr+0x6c/0x200 [f2fs]
  [<ffffffff811ae51b>] notify_change+0x1db/0x3a0
  [<ffffffff8118fbd0>] do_truncate+0x60/0xa0
  [<ffffffff8118fd95>] vfs_truncate+0x185/0x1b0
  [<ffffffff8118fe1c>] do_sys_truncate+0x5c/0xa0
  [<ffffffff8118ffee>] SyS_truncate+0xe/0x10
  [<ffffffff816e2b42>] system_call_fastpath+0x16/0x1b
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/data.c

@@ -199,7 +199,7 @@ struct page *find_data_page(struct inode *inode, pgoff_t index, bool sync)
 	if (dn.data_blkaddr == NEW_ADDR)
 		return ERR_PTR(-EINVAL);
 
-	page = grab_cache_page(mapping, index);
+	page = grab_cache_page_write_begin(mapping, index, AOP_FLAG_NOFS);
 	if (!page)
 		return ERR_PTR(-ENOMEM);
 
@@ -234,7 +234,7 @@ struct page *get_lock_data_page(struct inode *inode, pgoff_t index)
 	int err;
 
 repeat:
-	page = grab_cache_page(mapping, index);
+	page = grab_cache_page_write_begin(mapping, index, AOP_FLAG_NOFS);
 	if (!page)
 		return ERR_PTR(-ENOMEM);
 

fs/f2fs/inode.c

@@ -130,8 +130,7 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
 		inode->i_op = &f2fs_dir_inode_operations;
 		inode->i_fop = &f2fs_dir_operations;
 		inode->i_mapping->a_ops = &f2fs_dblock_aops;
-		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER_MOVABLE |
-				__GFP_ZERO);
+		mapping_set_gfp_mask(inode->i_mapping, GFP_F2FS_ZERO);
 	} else if (S_ISLNK(inode->i_mode)) {
 		inode->i_op = &f2fs_symlink_inode_operations;
 		inode->i_mapping->a_ops = &f2fs_dblock_aops;