ubi: fastmap: Allocate memory with GFP_NOFS in ubi_update_fastmap

Function ubi_update_fastmap could be called in IO context, for example:
 ubifs_writepage
  do_writepage
   ubifs_jnl_write_data
    write_head
     ubifs_wbuf_write_nolock
      ubifs_leb_write
       ubi_leb_write
        ubi_eba_write_leb
	 try_write_vid_and_data
	  ubi_wl_get_peb
	   ubi_update_fastmap
	    erase_block

So it's better to allocate memory with GFP_NOFS mode, in case waiting
page writeback(dead loop).

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/fastmap.c

@@ -20,7 +20,7 @@ static inline unsigned long *init_seen(struct ubi_device *ubi)
 	if (!ubi_dbg_chk_fastmap(ubi))
 		return NULL;
 
-	ret = bitmap_zalloc(ubi->peb_count, GFP_KERNEL);
+	ret = bitmap_zalloc(ubi->peb_count, GFP_NOFS);
 	if (!ret)
 		return ERR_PTR(-ENOMEM);
 
@@ -105,7 +105,7 @@ static struct ubi_vid_io_buf *new_fm_vbuf(struct ubi_device *ubi, int vol_id)
 	struct ubi_vid_io_buf *new;
 	struct ubi_vid_hdr *vh;
 
-	new = ubi_alloc_vid_buf(ubi, GFP_KERNEL);
+	new = ubi_alloc_vid_buf(ubi, GFP_NOFS);
 	if (!new)
 		goto out;
 
@@ -1403,7 +1403,7 @@ static int erase_block(struct ubi_device *ubi, struct ubi_wl_entry *e)
 	struct ubi_ec_hdr *ec_hdr;
 	long long ec = e->ec;
 
-	ec_hdr = kzalloc(ubi->ec_hdr_alsize, GFP_KERNEL);
+	ec_hdr = kzalloc(ubi->ec_hdr_alsize, GFP_NOFS);
 	if (!ec_hdr)
 		return -ENOMEM;
 
@@ -1459,7 +1459,7 @@ static int invalidate_fastmap(struct ubi_device *ubi)
 	ubi->fm = NULL;
 
 	ret = -ENOMEM;
-	fm = kzalloc(sizeof(*fm), GFP_KERNEL);
+	fm = kzalloc(sizeof(*fm), GFP_NOFS);
 	if (!fm)
 		goto out;
 
@@ -1548,7 +1548,7 @@ int ubi_update_fastmap(struct ubi_device *ubi)
 		return 0;
 	}
 
-	new_fm = kzalloc(sizeof(*new_fm), GFP_KERNEL);
+	new_fm = kzalloc(sizeof(*new_fm), GFP_NOFS);
 	if (!new_fm) {
 		up_write(&ubi->fm_eba_sem);
 		up_write(&ubi->work_sem);