[PATCH] f2fs: fix panic in f2fs_put_super

[sunshijie]

When thread A calls kill_f2fs_super, Thread A first executes the code sbi->node_inode = NULL;
Then thread A may submit a bio to the function iput(sbi->meta_inode);
Then thread A enters the process D state,
Now that the bio submitted by thread A is complete, it calls f2fs_write_end_io and may trigger null-ptr-deref in NODE_MAPPING.

Thread A                                          IRQ context
- f2fs_put_super
 - sbi->node_inode = NULL;
 - iput(sbi->meta_inode);
  - iput_final
   - write_inode_now
    - writeback_single_inode
     - __writeback_single_inode
      - filemap_fdatawait
       - filemap_fdatawait_range
        - __kcfi_typeid_free_transhuge_page
         - __filemap_fdatawait_range
          - wait_on_page_writeback
           - folio_wait_writeback
            - folio_wait_bit
             - folio_wait_bit_common
              - io_schedule

                                                  - __handle_irq_event_percpu
                                                   - ufs_qcom_mcq_esi_handler
                                                    - ufshcd_mcq_poll_cqe_nolock
                                                     - ufshcd_compl_one_cqe
                                                      - scsi_done
                                                       - scsi_done_internal
                                                        - blk_mq_complete_request
                                                         - scsi_complete
                                                          - scsi_finish_command
                                                           - scsi_io_completion
                                                            - scsi_end_request
                                                             - blk_update_request
                                                              - bio_endio
                                                               - f2fs_write_end_io
                                                                - NODE_MAPPING(sbi)

Signed-off-by: sunshijie <sunshijie@xxxxxxxxxx>
---
 fs/f2fs/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index adffc9b80a9c..62d4f229f601 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1642,9 +1642,9 @@ static void f2fs_put_super(struct super_block *sb)
 	f2fs_destroy_compress_inode(sbi);
 
 	iput(sbi->node_inode);
-	sbi->node_inode = NULL;
-
 	iput(sbi->meta_inode);
+
+	sbi->node_inode = NULL;
 	sbi->meta_inode = NULL;
 
 	mutex_unlock(&sbi->umount_mutex);
-- 
2.34.1