* Forwarded: [PATCH] f2fs: DEBUG: trace node folio lifecycle to diagnose write_end_io BUG
2026-05-14 20:19 [syzbot] [f2fs?] kernel BUG in f2fs_write_end_io (2) syzbot
@ 2026-05-14 23:35 ` syzbot
2026-05-15 1:00 ` Forwarded: [PATCH] f2fs: DEBUG: full lifecycle trace for node folio write-end-io BUG syzbot
2026-05-15 1:55 ` Forwarded: [PATCH] f2fs: don't BUG on node footer mismatch in f2fs_write_end_io syzbot
2 siblings, 0 replies; 4+ messages in thread
From: syzbot @ 2026-05-14 23:35 UTC (permalink / raw)
To: linux-kernel, syzkaller-bugs
For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.
***
Subject: [PATCH] f2fs: DEBUG: trace node folio lifecycle to diagnose 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 which path leaves
a node folio with folio->index != nid_of_node(folio) at writeback
time, triggering the BUG in f2fs_write_end_io() reported by syzbot.
Adds pr_info trace points at:
- f2fs_new_node_folio() - in-memory node folio construction
- __get_node_folio() - node folio lookup (cache or read)
- __get_node_folio() - synchronous footer sanity failure
- f2fs_finish_read_bio() - async read completion footer check
- f2fs_write_end_io() - write completion footer check
BUG_ON in f2fs_write_end_io() is intentionally retained so the
kernel halts at the failing folio and the preceding pr_info
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 | 19 ++++++++++++++-----
fs/f2fs/node.c | 5 +++++
2 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 8d4f1e75dee3..dc01a4fe089a 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -174,10 +174,17 @@ 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 rc=%d\n",
+ folio->index,
+ nid_of_node(folio),
+ ino_of_node(folio),
+ rc);
+ if (rc)
+ bio->bi_status = BLK_STS_IOERR;
+ }
if (finished)
folio_end_read(folio, bio->bi_status == BLK_STS_OK);
@@ -383,8 +390,10 @@ 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 rc=%d\n",
+ folio->index,nid_of_node(folio),ino_of_node(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..12a9774ac1df 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1423,6 +1423,8 @@ 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 node_folio: nid=%u ino=%lu ofs=%u\n",
+ dn->nid, dn->inode->i_ino, ofs);
if (!folio_test_uptodate(folio))
folio_mark_uptodate(folio);
if (folio_mark_dirty(folio))
@@ -1565,6 +1567,7 @@ 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))
@@ -1603,6 +1606,8 @@ 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
^ permalink raw reply related [flat|nested] 4+ messages in thread* Forwarded: [PATCH] f2fs: DEBUG: full lifecycle trace for node folio write-end-io BUG
2026-05-14 20:19 [syzbot] [f2fs?] kernel BUG in f2fs_write_end_io (2) syzbot
2026-05-14 23:35 ` Forwarded: [PATCH] f2fs: DEBUG: trace node folio lifecycle to diagnose write_end_io BUG syzbot
@ 2026-05-15 1:00 ` syzbot
2026-05-15 1:55 ` Forwarded: [PATCH] f2fs: don't BUG on node footer mismatch in f2fs_write_end_io syzbot
2 siblings, 0 replies; 4+ messages in thread
From: syzbot @ 2026-05-15 1:00 UTC (permalink / raw)
To: linux-kernel, syzkaller-bugs
For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.
***
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
^ permalink raw reply related [flat|nested] 4+ messages in thread* Forwarded: [PATCH] f2fs: don't BUG on node footer mismatch in f2fs_write_end_io
2026-05-14 20:19 [syzbot] [f2fs?] kernel BUG in f2fs_write_end_io (2) syzbot
2026-05-14 23:35 ` Forwarded: [PATCH] f2fs: DEBUG: trace node folio lifecycle to diagnose write_end_io BUG syzbot
2026-05-15 1:00 ` Forwarded: [PATCH] f2fs: DEBUG: full lifecycle trace for node folio write-end-io BUG syzbot
@ 2026-05-15 1:55 ` syzbot
2 siblings, 0 replies; 4+ messages in thread
From: syzbot @ 2026-05-15 1:55 UTC (permalink / raw)
To: linux-kernel, syzkaller-bugs
For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.
***
Subject: [PATCH] f2fs: don't BUG on node footer mismatch in f2fs_write_end_io
Author: kartikey406@gmail.com
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
Syzbot reports a recurrence of the kernel BUG in f2fs_write_end_io:
kernel BUG at fs/f2fs/data.c:388!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 15 Comm: ksoftirqd/0 PREEMPT_{RT,(full)}
RIP: 0010:f2fs_write_end_io+0x16df/0x1740
Call Trace:
blk_update_request+0x57e/0xe60
blk_mq_end_request+0x3e/0x70
blk_done_softirq+0x10a/0x160
handle_softirqs+0x1de/0x6d0
run_ksoftirqd+0x52/0x180
Commit 50ac3ecd8e05 ("f2fs: fix to do sanity check on node footer
in {read,write}_end_io") added f2fs_sanity_check_node_footer() to
both end_io paths to catch corrupted node footers reachable from
fuzzed on-disk images. In f2fs_write_end_io(), however, the
existing
f2fs_bug_on(sbi, folio->index != nid_of_node(folio));
was left in place immediately after the new helper call. The
helper detects the mismatch, sets SBI_NEED_FSCK and emits a
ratelimited warning, but its return value is discarded and the
following f2fs_bug_on() panics on the exact same condition.
Tracing the reproducer confirms the failure path. A node folio
with index=11 is looked up via __get_node_folio(), the
synchronous sanity check at page_hit fails with -EFSCORRUPTED
and out_err clears uptodate but leaves the dirty bit set from
the folio's earlier lifecycle. A subsequent read_node_folio()
fails with the same error (footer_nid=0, ino=0), and
folio_end_read(folio, false) does not clear dirty either. The
writeback iterator then finds the still-dirty folio via the
PAGECACHE_TAG_DIRTY tag and submits it. f2fs_write_end_io()
observes folio->index=11 with nid_of_node(folio)=0 and panics
from softirq context via blk_done_softirq, even though
f2fs_sanity_check_node_footer() has already correctly identified
the corruption and would have signalled it via its return value.
A filesystem inconsistency reachable from a mounted image must
not panic the kernel. Mirror the handling already used in
f2fs_finish_read_bio(): capture the helper's return value and
mark the bio with BLK_STS_IOERR on mismatch instead of issuing
BUG_ON. SBI_NEED_FSCK is set by the helper, so fsck.f2fs will
repair the inconsistency on the next mount.
Reported-by: syzbot+4af46ee83100e99bce09@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
Fixes: 50ac3ecd8e05 ("f2fs: fix to do sanity check on node footer in {read,write}_end_io")
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
fs/f2fs/data.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 8d4f1e75dee3..c149b0ccf22d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -382,11 +382,11 @@ static void f2fs_write_end_io(struct bio *bio)
STOP_CP_REASON_WRITE_FAIL);
}
- if (is_node_folio(folio)) {
- f2fs_sanity_check_node_footer(sbi, folio,
- folio->index, NODE_TYPE_REGULAR, true);
- f2fs_bug_on(sbi, folio->index != nid_of_node(folio));
- }
+ if (is_node_folio(folio) &&
+ f2fs_sanity_check_node_footer(sbi, folio,
+ folio->index, NODE_TYPE_REGULAR, true))
+ bio->bi_status = BLK_STS_IOERR;
+
if (f2fs_in_warm_node_list(folio))
f2fs_del_fsync_node_entry(sbi, folio);
--
2.43.0
^ permalink raw reply related [flat|nested] 4+ messages in thread