[PATCH v2 2/2] jfs: wait for in-flight log I/O before freeing lbufs in lbmLogShutdown

Tristan Madani
2026-05-05T12:33:34Z

lbmLogShutdown() frees log buffer (lbuf) pages and structures from
log->lbuf_free. However, BIO completions (lbmIODone) may still be
executing in softirq context when lbmLogShutdown() runs, because
lbmIODone accesses lbuf fields (l_flag, l_log, l_freelist) before
returning the buffer to the freelist.

If lbmLogShutdown() runs concurrently with lbmIODone in-flight,
it can free an lbuf that lbmIODone is still accessing -- resulting
in a use-after-free.

Fix this by adding an atomic io_count to struct jfs_log that tracks
in-flight BIO operations. lbmStartIO increments it before submit_bio
(or before calling lbmIODone directly for no_integrity mode), and
lbmIODone decrements it after all lbuf accesses are complete.
lbmLogShutdown waits for io_count to reach zero before freeing any
lbufs.

Reported-by: syzbot+c244f4a09ca85dd2ebc1@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c244f4a09ca85dd2ebc1
Reported-by: syzbot+885a4f3281b8d99c48d8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=885a4f3281b8d99c48d8
Fixes: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
fs/jfs/jfs_logmgr.c | 12 ++++++++++++
fs/jfs/jfs_logmgr.h | 2 ++
2 files changed, 14 insertions(+)

diff --git a/fs/jfs/jfs_logmgr.c b/fs/jfs/jfs_logmgr.c
index 306165e61438c..95e95f71ec0fa 100644
--- a/fs/jfs/jfs_logmgr.c
+++ b/fs/jfs/jfs_logmgr.c
@@ -1804,6 +1804,8 @@ static int lbmLogInit(struct jfs_log * log)
* avoid deadlock here.
*/
init_waitqueue_head(&log->free_wait);
+ atomic_set(&log->io_count, 0);
+ init_waitqueue_head(&log->io_done_wait);

log->lbuf_free = NULL;

@@ -1855,6 +1857,9 @@ static void lbmLogShutdown(struct jfs_log * log)

jfs_info("lbmLogShutdown: log:0x%p", log);

+ /* Wait for all in-flight log I/O to complete */
+ wait_event(log->io_done_wait, !atomic_read(&log->io_count));
+
lbuf = log->lbuf_free;
while (lbuf) {
struct lbuf *next = lbuf->l_freelist;
@@ -1976,6 +1981,8 @@ static int lbmRead(struct jfs_log * log, int pn, struct lbuf ** bpp)

bio->bi_end_io = lbmIODone;
bio->bi_private = bp;
+
+ atomic_inc(&log->io_count);
/*check if journaling to disk has been disabled*/
if (log->no_integrity) {
bio->bi_iter.bi_size = 0;
@@ -2123,6 +2130,8 @@ static void lbmStartIO(struct lbuf * bp)
bio->bi_end_io = lbmIODone;
bio->bi_private = bp;

+ atomic_inc(&log->io_count);
+
/* check if journaling to disk has been disabled */
if (log->no_integrity) {
bio->bi_iter.bi_size = 0;
@@ -2299,6 +2308,9 @@ static void lbmIODone(struct bio *bio)
out:
bp->l_flag |= lbmDONE;
LCACHE_UNLOCK(flags);
+
+ if (atomic_dec_and_test(&bp->l_log->io_count))
+ wake_up(&bp->l_log->io_done_wait);
}

int jfsIOWait(void *arg)
diff --git a/fs/jfs/jfs_logmgr.h b/fs/jfs/jfs_logmgr.h
index 09e0ef6aeccef..cbf38ed27c950 100644
--- a/fs/jfs/jfs_logmgr.h
+++ b/fs/jfs/jfs_logmgr.h
@@ -367,6 +367,8 @@ struct jfs_log {

struct lbuf *lbuf_free; /* 4: free lbufs */
wait_queue_head_t free_wait; /* 4: */
+ atomic_t io_count; /* in-flight log I/O count */
+ wait_queue_head_t io_done_wait; /* wait for io_count == 0 */

/* log write */
int logtid; /* 4: log tid */
--
2.47.3