Forwarded: [PATCH] f2fs: DEBUG: full lifecycle trace for node folio write-end-io BUG

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Subject: [PATCH] f2fs: DEBUG: full lifecycle trace for node folio write-end-io BUG
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


Not for upstream. Instrumentation to identify how a node folio
with mismatched folio->index and nid_of_node(folio) reaches
f2fs_write_end_io and triggers the BUG_ON reported by syzbot.

Previous test run confirmed the read-side sanity check fires
(rc=-EFSCORRUPTED) yet the same folio still reaches writeback.
This round adds traces at every cache lifecycle event so the
leak path can be pinned down:

  - f2fs_finish_read_bio  - async read footer check, page state
  - f2fs_write_end_io     - write footer check, page state
  - f2fs_new_node_folio   - entry, after grab, after fill_footer,
                            after mark_dirty
  - read_node_folio       - entry, with current page state
  - __get_node_folio      - entry and after grab, page state
  - __get_node_folio      - sync sanity failure on page_hit

Each trace logs folio->index, footer nid/ino, and the relevant
page flags (uptodate, dirty, writeback, refcount) so the journey
of a single NID can be reconstructed across read failure, cache
reuse, and writeback submission.

BUG_ON in f2fs_write_end_io() is intentionally retained so the
kernel halts at the failing folio and the preceding trace output
appears in the syzbot console log.

Link: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
Not-Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/f2fs/data.c | 16 +++++++++++-----
 fs/f2fs/node.c | 19 ++++++++++++++++++-
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 8d4f1e75dee3..571ba13916ef 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -174,10 +174,14 @@ static void f2fs_finish_read_bio(struct bio *bio, bool in_task)
 			dec_page_count(F2FS_F_SB(folio), __read_io_type(folio));
 
 		if (bio->bi_status == BLK_STS_OK &&
-			F2FS_F_SB(folio)->node_inode && is_node_folio(folio) &&
-			f2fs_sanity_check_node_footer(F2FS_F_SB(folio),
-				folio, folio->index, NODE_TYPE_REGULAR, true))
-			bio->bi_status = BLK_STS_IOERR;
+			F2FS_F_SB(folio)->node_inode && is_node_folio(folio)) {
+			int rc = f2fs_sanity_check_node_footer(F2FS_F_SB(folio),
+			                                       folio, folio->index, NODE_TYPE_REGULAR, true);
+			pr_info("f2fs-dbg: READ end_io: index=%lu footer_nid=%u ino=%u uptodate=%d dirty=%d rc=%d\n",
+				folio->index,nid_of_node(folio),ino_of_node(folio),folio_test_uptodate(folio),folio_test_dirty(folio),rc);
+			if (rc)
+				bio->bi_status = BLK_STS_IOERR;
+		}
 
 		if (finished)
 			folio_end_read(folio, bio->bi_status == BLK_STS_OK);
@@ -383,8 +387,10 @@ static void f2fs_write_end_io(struct bio *bio)
 		}
 
 		if (is_node_folio(folio)) {
-			f2fs_sanity_check_node_footer(sbi, folio,
+			int rc = f2fs_sanity_check_node_footer(sbi, folio,
 				folio->index, NODE_TYPE_REGULAR, true);
+			pr_info("f2fs-dbg: WRITE end_io: index=%lu footer_nid=%u ino=%u uptodate=%d dirty=%d rc=%d\n",
+				folio->index,nid_of_node(folio),ino_of_node(folio),folio_test_uptodate(folio),folio_test_dirty(folio),rc);
 			f2fs_bug_on(sbi, folio->index != nid_of_node(folio));
 		}
 		if (f2fs_in_warm_node_list(folio))
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 4e5bd9e4cfc3..d38b32fe7ee9 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1384,6 +1384,8 @@ struct folio *f2fs_new_node_folio(struct dnode_of_data *dn, unsigned int ofs)
 	struct folio *folio;
 	int err;
 
+	pr_info("f2fs-dbg: NEW entry: nid=%u ino=%lu ofs=%u\n",
+		dn->nid, dn->inode->i_ino, ofs);
 	if (unlikely(is_inode_flag_set(dn->inode, FI_NO_ALLOC)))
 		return ERR_PTR(-EPERM);
 
@@ -1391,6 +1393,8 @@ struct folio *f2fs_new_node_folio(struct dnode_of_data *dn, unsigned int ofs)
 	if (IS_ERR(folio))
 		return folio;
 
+	pr_info("f2fs-dbg: NEW grabbed: nid=%u uptodate=%d dirty=%d writeback=%d refcount=%d\n",
+		dn->nid,folio_test_uptodate(folio),folio_test_dirty(folio),folio_test_writeback(folio),folio_ref_count(folio));
 	if (unlikely((err = inc_valid_node_count(sbi, dn->inode, !ofs))))
 		goto fail;
 
@@ -1423,10 +1427,14 @@ struct folio *f2fs_new_node_folio(struct dnode_of_data *dn, unsigned int ofs)
 	f2fs_folio_wait_writeback(folio, NODE, true, true);
 	fill_node_footer(folio, dn->nid, dn->inode->i_ino, ofs, true);
 	set_cold_node(folio, S_ISDIR(dn->inode->i_mode));
+	pr_info("f2fs-dbg: NEW after fill_footer: nid=%u footer_nid=%u footer_ino=%u\n",
+		dn->nid, nid_of_node(folio), ino_of_node(folio));
 	if (!folio_test_uptodate(folio))
 		folio_mark_uptodate(folio);
-	if (folio_mark_dirty(folio))
+	if (folio_mark_dirty(folio)) {
+		pr_info("f2fs-dbg: NEW marked dirty: nid=%u\n", dn->nid);
 		dn->node_changed = true;
+	}
 
 	if (f2fs_has_xattr_block(ofs))
 		f2fs_i_xnid_write(dn->inode, dn->nid);
@@ -1459,6 +1467,10 @@ static int read_node_folio(struct folio *folio, blk_opf_t op_flags)
 	};
 	int err;
 
+	 pr_info("f2fs-dbg: read_node_folio entry: index=%lu uptodate=%d dirty=%d\n",
+            folio->index,
+            folio_test_uptodate(folio),
+            folio_test_dirty(folio));
 	if (folio_test_uptodate(folio)) {
 		if (!f2fs_inode_chksum_verify(sbi, folio)) {
 			folio_clear_uptodate(folio);
@@ -1565,6 +1577,7 @@ static struct folio *__get_node_folio(struct f2fs_sb_info *sbi, pgoff_t nid,
 	struct folio *folio;
 	int err;
 
+	pr_info("f2fs-dbg: GET node_folio: nid=%lu ntype=%d\n", nid, ntype);
 	if (!nid)
 		return ERR_PTR(-ENOENT);
 	if (f2fs_check_nid_range(sbi, nid))
@@ -1574,6 +1587,8 @@ static struct folio *__get_node_folio(struct f2fs_sb_info *sbi, pgoff_t nid,
 	if (IS_ERR(folio))
 		return folio;
 
+	pr_info("f2fs-dbg: GET grabbed: nid=%lu uptodate=%d dirty=%d writeback=%d refcount=%d\n",
+		nid,folio_test_uptodate(folio),folio_test_dirty(folio),folio_test_writeback(folio),folio_ref_count(folio));
 	err = read_node_folio(folio, 0);
 	if (err < 0)
 		goto out_put_err;
@@ -1603,6 +1618,8 @@ static struct folio *__get_node_folio(struct f2fs_sb_info *sbi, pgoff_t nid,
 	err = f2fs_sanity_check_node_footer(sbi, folio, nid, ntype, false);
 	if (!err)
 		return folio;
+	pr_info("f2fs-dbg: SYNC sanity fail: nid=%lu footer_nid=%u ino=%u err=%d\n",
+		nid,nid_of_node(folio),ino_of_node(folio),err);
 out_err:
 	folio_clear_uptodate(folio);
 out_put_err:
-- 
2.43.0