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.

---
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(-)

index 0ca3110d6386..8b3225bd08ed 100644
@@ -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

Andrew, please stop sending this patch upstream.

I found a problem with changing the error path in this patch in another error injection test, so I would like to create a revised version.

The other two bug fix patches I have sent will not be affected.

Thanks,
Ryusuke Konishi

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 uniformly calling nilfs_segctor_abort_construction() on failure of each step in the loop in nilfs_segctor_do_construct(), having it clean up logs and segment usages according to progress, and correcting the conditions for calling nilfs_redirty_inodes() to ensure that the NILFS_I_COLLECTED flag is cleared.

---
Andrew, please apply this as a bug fix instead of the one dropped recently.

This fixes error path flaws of the log writing function, 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.

v1->v2: fixed a regression that caused unexpected cleanup when
handling an error at a stage where no logs were ready.

Thanks,
Ryusuke Konishi

 fs/nilfs2/segment.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

index 0ca3110d6386..871ec35ea8e8 100644
@@ -1812,6 +1812,9 @@ static void nilfs_segctor_abort_construction(struct nilfs_sc_info *sci,
 	nilfs_abort_logs(&logs, ret ? : err);
 
 	list_splice_tail_init(&sci->sc_segbufs, &logs);
+	if (list_empty(&logs))
+		return; /* if the first segment buffer preparation failed */
+
 	nilfs_cancel_segusage(&logs, nilfs->ns_sufile);
 	nilfs_free_incomplete_logs(&logs, nilfs);
 

@@ -2056,7 +2059,7 @@ 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 +2123,9 @@ 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