f2fs: allow readdir() to be interrupted

This patch follows ext4 to allow readdir() in large empty directory to
be interrupted. Referenced commit of ext4: 1f60fbe7 ("ext4: allow
readdir()'s of large empty directories to be interrupted").
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/dir.c

@@ -10,6 +10,7 @@
  */
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
+#include <linux/sched/signal.h>
 #include "f2fs.h"
 #include "node.h"
 #include "acl.h"
@@ -875,6 +876,14 @@ static int f2fs_readdir(struct file *file, struct dir_context *ctx)
 				min(npages - n, (pgoff_t)MAX_DIR_RA_PAGES));
 
 	for (; n < npages; n++) {
+
+		/* allow readdir() to be interrupted */
+		if (fatal_signal_pending(current)) {
+			err = -ERESTARTSYS;
+			goto out_free;
+		}
+		cond_resched();
+
 		dentry_page = get_lock_data_page(inode, n, false);
 		if (IS_ERR(dentry_page)) {
 			err = PTR_ERR(dentry_page);