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Subject: Re: [syzbot] [jfs?] KASAN: slab-use-after-free Read in lbmIODone
Author: tristmd@gmail.com

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

diff --git a/fs/jfs/jfs_logmgr.c b/fs/jfs/jfs_logmgr.c
index XXXXXXX..XXXXXXX 100644
--- a/fs/jfs/jfs_logmgr.c
+++ b/fs/jfs/jfs_logmgr.c
@@ -1805,6 +1805,8 @@ static int lbmLogInit(struct jfs_log * log)
 	 */
 	init_waitqueue_head(&log->free_wait);
 
+	atomic_set(&log->io_count, 0);
+
 	log->lbuf_free = NULL;
 
 	for (i = 0; i < LOGPAGES;) {
@@ -1855,6 +1857,8 @@ static void lbmLogShutdown(struct jfs_log * log)
 
 	jfs_info("lbmLogShutdown: log:0x%p", log);
 
+	wait_var_event(&log->io_count, atomic_read(&log->io_count) == 0);
+
 	lbuf = log->lbuf_free;
 	while (lbuf) {
 		struct lbuf *next = lbuf->l_freelist;
@@ -2128,6 +2132,7 @@ static void lbmStartIO(struct lbuf * bp)
 		bio->bi_iter.bi_size = 0;
 		lbmIODone(bio);
 	} else {
+		atomic_inc(&log->io_count);
 		submit_bio(bio);
 		INCREMENT(lmStat.submitted);
 	}
@@ -2170,12 +2175,16 @@ static void lbmIODone(struct bio *bio)
 	struct lbuf *nextbp, *tail;
 	struct jfs_log *log;
 	unsigned long flags;
+	int is_write;
 
 	/*
 	 * get back jfs buffer bound to the i/o buffer
 	 */
 	jfs_info("lbmIODone: bp:0x%p flag:0x%x", bp, bp->l_flag);
 
+	log = bp->l_log;
+	is_write = !(bp->l_flag & lbmREAD);
+
 	LCACHE_LOCK(flags);		/* disable+lock */
 
 	if (bio->bi_status) {
@@ -2214,7 +2223,6 @@ static void lbmIODone(struct bio *bio)
 	INCREMENT(lmStat.pagedone);
 
 	/* update committed lsn */
-	log = bp->l_log;
 	log->clsn = (bp->l_pn << L2LOGPSIZE) + bp->l_ceor;
 
 	if (bp->l_flag & lbmDIRECT) {
@@ -2299,6 +2307,10 @@ static void lbmIODone(struct bio *bio)
 out:
 	bp->l_flag |= lbmDONE;
 	LCACHE_UNLOCK(flags);
+
+	if (is_write && !log->no_integrity)
+		if (atomic_dec_and_test(&log->io_count))
+			wake_up_var(&log->io_count);
 }
 
 int jfsIOWait(void *arg)
diff --git a/fs/jfs/jfs_logmgr.h b/fs/jfs/jfs_logmgr.h
index XXXXXXX..XXXXXXX 100644
--- a/fs/jfs/jfs_logmgr.h
+++ b/fs/jfs/jfs_logmgr.h
@@ -400,6 +400,8 @@ struct jfs_log {
 	uuid_t uuid;		/* 16: 128-bit uuid of log device */
 
 	int no_integrity;	/* 3: flag to disable journaling to disk */
+
+	atomic_t io_count;	/* outstanding I/O count for shutdown drain */
 };
 
 /*