[Ocfs2-devel] [PATCH] ocfs2: fix a null pointer derefrence in ocfs2_block_group_clear_bits()

[lishan]

A NULL pointer panic dereference in ocfs2_block_group_clear_bits() happen again.
The information of NULL pointer stack as follows:

PID: 81866  TASK: ffffa07c3c21ae80  CPU: 66  COMMAND: "fallocate"
  #0 [ffff0000b4d6b0b0] machine_kexec at ffff0000800a2954
  #1 [ffff0000b4d6b110] __crash_kexec at ffff0000801bab34
  #2 [ffff0000b4d6b2a0] panic at ffff0000800f02cc
  #3 [ffff0000b4d6b380] die at ffff00008008f6ac
  #4 [ffff0000b4d6b3d0] bug_handler at ffff00008008f744
  #5 [ffff0000b4d6b400] brk_handler at ffff000080085d1c
  #6 [ffff0000b4d6b420] do_debug_exception at ffff000080081194
  #7 [ffff0000b4d6b630] el1_dbg at ffff00008008332c
      PC: ffff00000190e9c0  [_ocfs2_free_suballoc_bits+1608]
      LR: ffff00000190e990  [_ocfs2_free_suballoc_bits+1560]
      SP: ffff0000b4d6b640  PSTATE: 60400009
     X29: ffff0000b4d6b650  X28: 0000000000000000  X27: 00000000000052f3
     X26: ffff807c511a9570  X25: ffff807ca0054000  X24: 00000000000052f2
     X23: 0000000000000001  X22: ffff807c7cde7a90  X21: ffff0000811d9000
     X20: ffff807c5e7d2000  X19: ffff00000190c768  X18: 0000000000000000
     X17: 0000000000000000  X16: ffff000080a032f0  X15: 0000000000000000
     X14: ffffffffffffffff  X13: fffffffffffffff7  X12: ffffffffffffffff
     X11: 0000000000000038  X10: 0101010101010101   X9: ffffffffffffffff
      X8: 7f7f7f7f7f7f7f7f   X7: 0000000000000000   X6: 0000000000000080
      X5: 0000000000000000   X4: 0000000000000002   X3: ffff00000199f390
      X2: a603c08321456e00   X1: ffff807c7cde7a90   X0: 0000000000000000
  #8 [ffff0000b4d6b650] _ocfs2_free_suballoc_bits at ffff00000190e9bc [ocfs2]
  #9 [ffff0000b4d6b710] _ocfs2_free_clusters at ffff0000019110d4 [ocfs2]
 #10 [ffff0000b4d6b790] ocfs2_free_clusters at ffff000001913e94 [ocfs2]
 #11 [ffff0000b4d6b7d0] __ocfs2_flush_truncate_log at ffff0000018b5294 [ocfs2]
 #12 [ffff0000b4d6b8a0] ocfs2_remove_btree_range at ffff0000018bb34c [ocfs2]
 #13 [ffff0000b4d6b960] ocfs2_commit_truncate at ffff0000018bc76c [ocfs2]
 #14 [ffff0000b4d6ba60] ocfs2_wipe_inode at ffff0000018e57bc [ocfs2]
 #15 [ffff0000b4d6bb00] ocfs2_evict_inode at ffff0000018e5db8 [ocfs2]
 #16 [ffff0000b4d6bb70] evict at ffff000080365040
 #17 [ffff0000b4d6bba0] iput at ffff0000803655d8
 #18 [ffff0000b4d6bbe0] ocfs2_dentry_iput at ffff0000018c60a0 [ocfs2]
 #19 [ffff0000b4d6bc30] dentry_unlink_inode at ffff00008035ef58
 #20 [ffff0000b4d6bc50] __dentry_kill at ffff000080360384
 #21 [ffff0000b4d6bc80] dentry_kill at ffff000080360670
 #22 [ffff0000b4d6bcb0] dput at ffff00008036093c
 #23 [ffff0000b4d6bcf0] __fput at ffff000080343930
 #24 [ffff0000b4d6bd40] ____fput at ffff000080343aac
 #25 [ffff0000b4d6bd60] task_work_run at ffff0000801172fc

The direct panic reason is that bh2jh (group_bh)-> b_committed_data is null.
It is presumed that the network was disconnected during the write process,
causing the transaction abort. as follows:
jbd2_journal_abort
  .......
  jbd2_journal_commit_transaction
    jh->b_committed_data = NULL;

_ocfs2_free_suballoc_bits
  ocfs2_block_group_clear_bits
    // undo_bg is now set to null
    BUG_ON(!undo_bg);

When applying for free space, if b_committed_data is null,
it will be directly occupied, as follows:
ocfs2_cluster_group_search
  ocfs2_block_group_find_clear_bits
    ocfs2_test_bg_bit_allocatable:
      bg = (struct ocfs2_group_desc *) bh2jh(bg_bh)->b_committed_data;
      if (bg)
        ret = !ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap);
      else
        ret = 1;
b_committed_data is an intermediate state backup for bitmap transaction commits,
newly applied space can overwrite previous dirty data,
so, I think, while free clusters, if b_committed_data is null, ignore it.
Host panic directly, too violent.

Signed-off-by: Shan Li <lishan24 at huawei.com>
Reviewed-by: Jun Piao <piaojun at huawei.com>
---
 fs/ocfs2/suballoc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index 939df99d2dec..aaf1b3cbd984 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -2412,14 +2412,19 @@ static int ocfs2_block_group_clear_bits(handle_t *handle,
 	if (undo_fn) {
 		spin_lock(&jh->b_state_lock);
 		undo_bg = (struct ocfs2_group_desc *) jh->b_committed_data;
-		BUG_ON(!undo_bg);
+		if (!undo_bg)
+			mlog(ML_NOTICE, "%s: group descriptor # %llu (device %s) journal "
+					"b_committed_data had been cleared.\n",
+					OCFS2_SB(alloc_inode->i_sb)->uuid_str,
+					(unsigned long long)le64_to_cpu(bg->bg_blkno),
+					alloc_inode->i_sb->s_id);
 	}

 	tmp = num_bits;
 	while(tmp--) {
 		ocfs2_clear_bit((bit_off + tmp),
 				(unsigned long *) bg->bg_bitmap);
-		if (undo_fn)
+		if (undo_fn && undo_bg)
 			undo_fn(bit_off + tmp,
 				(unsigned long *) undo_bg->bg_bitmap);
 	}
-- 
2.19.1