linux-kernel - [PATCH 1/2] ubifs: Re-statistic cleaned znode count if commit failed

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Date:   Fri, 18 Nov 2022 17:02:35 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     <richard@....at>, <miquel.raynal@...tlin.com>,
        <s.hauer@...gutronix.de>
CC:     <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <chengzhihao1@...wei.com>, <yi.zhang@...wei.com>
Subject: [PATCH 1/2] ubifs: Re-statistic cleaned znode count if commit failed

Dirty znodes will be written on flash in committing process with
following states:

	      process A			|  znode state
------------------------------------------------------
do_commit				| DIRTY_ZNODE
  ubifs_tnc_start_commit		| DIRTY_ZNODE
   get_znodes_to_commit			| DIRTY_ZNODE | COW_ZNODE
    layout_commit			| DIRTY_ZNODE | COW_ZNODE
     fill_gap                           | 0
  write master				| 0 or OBSOLETE_ZNODE

	      process B			|  znode state
------------------------------------------------------
do_commit				| DIRTY_ZNODE[1]
  ubifs_tnc_start_commit		| DIRTY_ZNODE
   get_znodes_to_commit			| DIRTY_ZNODE | COW_ZNODE
  ubifs_tnc_end_commit			| DIRTY_ZNODE | COW_ZNODE
   write_index                          | 0
  write master				| 0 or OBSOLETE_ZNODE[2] or
					| DIRTY_ZNODE[3]

[1] znode is dirtied without concurrent committing process
[2] znode is copied up (re-dirtied by other process) before cleaned
    up in committing process
[3] znode is re-dirtied after cleaned up in committing process

Currently, the clean znode count is updated in free_obsolete_znodes(),
which is called only in normal path. If do_commit failed, clean znode
count won't be updated, which triggers a failure ubifs assertion[4] in
ubifs_tnc_close():
 ubifs_assert_failed [ubifs]: UBIFS assert failed: freed == n

[4] Commit 380347e9ca7682 ("UBIFS: Add an assertion for clean_zn_cnt").

Fix it by re-statisticing cleaned znode count in tnc_destroy_cnext().

Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216704
Fixes: 1e51764a3c2a ("UBIFS: add new flash file system")
Signed-off-by: Zhihao Cheng <chengzhihao1@...wei.com>
---
 fs/ubifs/tnc.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/ubifs/tnc.c b/fs/ubifs/tnc.c
index 488f3da7a6c6..2df56bbc6865 100644
--- a/fs/ubifs/tnc.c
+++ b/fs/ubifs/tnc.c
@@ -3053,6 +3053,21 @@ static void tnc_destroy_cnext(struct ubifs_info *c)
 		cnext = cnext->cnext;
 		if (ubifs_zn_obsolete(znode))
 			kfree(znode);
+		else if (!ubifs_zn_cow(znode)) {
+			/*
+			 * Don't forget to update clean znode count after
+			 * committing failed, because ubifs will check this
+			 * count while closing tnc. Non-obsolete znode could
+			 * be re-dirtied during committing process, so dirty
+			 * flag is untrustable. The flag 'COW_ZNODE' is set
+			 * for each dirty znode before committing, and it is
+			 * cleared as long as the znode become clean, so we
+			 * can statistic clean znode count according to this
+			 * flag.
+			 */
+			atomic_long_inc(&c->clean_zn_cnt);
+			atomic_long_inc(&ubifs_clean_zn_cnt);
+		}
 	} while (cnext && cnext != c->cnext);
 }
 
-- 
2.31.1