linux-kernel - [PATCH] nilfs2: fix state management in error path of log writing function

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Message-Id: <20240807230742.11151-1-konishi.ryusuke@gmail.com>
Date: Thu,  8 Aug 2024 08:07:42 +0900
From: Ryusuke Konishi <konishi.ryusuke@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-nilfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] nilfs2: fix state management in error path of log writing function

After commit a694291a6211 ("nilfs2: separate wait function from
nilfs_segctor_write") was applied, the log writing function
nilfs_segctor_do_construct() was able to issue I/O requests
continuously even if user data blocks were split into multiple logs
across segments, but two potential flaws were introduced in its error
handling.

First, if nilfs_segctor_begin_construction() fails while creating the
second or subsequent logs, the log writing function returns without
calling nilfs_segctor_abort_construction(), so the writeback flag set
on pages/folios will remain uncleared.  This causes page cache
operations to hang waiting for the writeback flag.  For example,
truncate_inode_pages_final(), which is called via nilfs_evict_inode()
when an inode is evicted from memory, will hang.

Second, the NILFS_I_COLLECTED flag set on normal inodes remain
uncleared.  As a result, if the next log write involves checkpoint
creation, that's fine, but if a partial log write is performed that
does not, inodes with NILFS_I_COLLECTED set are erroneously removed
from the "sc_dirty_files" list, and their data and b-tree blocks may
not be written to the device, corrupting the block mapping.

Fix these issues by correcting the jump destination of the error
branch in nilfs_segctor_do_construct() and the condition for calling
nilfs_redirty_inodes(), which clears the NILFS_I_COLLECTED flag.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@...il.com>
Fixes: a694291a6211 ("nilfs2: separate wait function from nilfs_segctor_write")
Tested-by: Ryusuke Konishi <konishi.ryusuke@...il.com>
Cc: stable@...r.kernel.org
---
Hi Andrew, please apply this as a bug fix.

This fixes error path flaws of the log writing function that was
discovered during error injection testing, which could lead to a hang
due to the writeback flag not being cleared on folios, and potential
filesystem corruption due to missing blocks in the log after an error.

Thanks,
Ryusuke Konishi

 fs/nilfs2/segment.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 0ca3110d6386..8b3225bd08ed 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -2056,7 +2056,7 @@ static int nilfs_segctor_do_construct(struct nilfs_sc_info *sci, int mode)

 		err = nilfs_segctor_begin_construction(sci, nilfs);
 		if (unlikely(err))
-			goto out;
+			goto failed;

 		/* Update time stamp */
 		sci->sc_seg_ctime = ktime_get_real_seconds();
@@ -2120,10 +2120,9 @@ static int nilfs_segctor_do_construct(struct nilfs_sc_info *sci, int mode)
 	return err;

  failed_to_write:
-	if (sci->sc_stage.flags & NILFS_CF_IFILE_STARTED)
-		nilfs_redirty_inodes(&sci->sc_dirty_files);
-
  failed:
+	if (mode == SC_LSEG_SR && nilfs_sc_cstage_get(sci) >= NILFS_ST_IFILE)
+		nilfs_redirty_inodes(&sci->sc_dirty_files);
 	if (nilfs_doing_gc())
 		nilfs_redirty_inodes(&sci->sc_gc_inodes);
 	nilfs_segctor_abort_construction(sci, nilfs, err);
-- 
2.34.1