The transaction manager initialization in txInit() was not properly
initializing TxBlock[0].waitor waitqueue, causing a crash when
txEnd(0) is called on read-only filesystems.

When a filesystem is mounted read-only, txBegin() returns tid=0 to
indicate no transaction. However, txEnd(0) still gets called and
tries to access TxBlock[0].waitor via tid_to_tblock(0), but this
waitqueue was never initialized because the initialization loop
started at index 1 instead of 0.

This causes a 'non-static key' lockdep warning and system crash:
  INFO: trying to register non-static key in txEnd

Fix by ensuring all transaction blocks including TxBlock[0] have
their waitqueues properly initialized during txInit().

Reported-by: syzbot+c4f3462d8b2ad7977bea@syzkaller.appspotmail.com

Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
---
 fs/jfs/jfs_txnmgr.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/jfs/jfs_txnmgr.c b/fs/jfs/jfs_txnmgr.c
index be17e3c43582..7840a03e5bcb 100644
--- a/fs/jfs/jfs_txnmgr.c
+++ b/fs/jfs/jfs_txnmgr.c
@@ -272,14 +272,15 @@ int txInit(void)
 	if (TxBlock == NULL)
 		return -ENOMEM;
 
-	for (k = 1; k < nTxBlock - 1; k++) {
-		TxBlock[k].next = k + 1;
+	for (k = 0; k < nTxBlock; k++) {
 		init_waitqueue_head(&TxBlock[k].gcwait);
 		init_waitqueue_head(&TxBlock[k].waitor);
 	}
+
+	for (k = 1; k < nTxBlock - 1; k++) {
+		TxBlock[k].next = k + 1;
+	}
 	TxBlock[k].next = 0;
-	init_waitqueue_head(&TxBlock[k].gcwait);
-	init_waitqueue_head(&TxBlock[k].waitor);
 
 	TxAnchor.freetid = 1;
 	init_waitqueue_head(&TxAnchor.freewait);
-- 
2.34.1

On 8/24/25 3:13PM, Shaurya Rane wrote:
> The transaction manager initialization in txInit() was not properly
> initializing TxBlock[0].waitor waitqueue, causing a crash when
> txEnd(0) is called on read-only filesystems.
> 
> When a filesystem is mounted read-only, txBegin() returns tid=0 to
> indicate no transaction. However, txEnd(0) still gets called and
> tries to access TxBlock[0].waitor via tid_to_tblock(0), but this
> waitqueue was never initialized because the initialization loop
> started at index 1 instead of 0.
> 
> This causes a 'non-static key' lockdep warning and system crash:
>    INFO: trying to register non-static key in txEnd
> 
> Fix by ensuring all transaction blocks including TxBlock[0] have
> their waitqueues properly initialized during txInit().
> 
> Reported-by: syzbot+c4f3462d8b2ad7977bea@syzkaller.appspotmail.com
> 
> Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>

Looks good, and the code even looks prettier. Applying and testing.

Thanks,
Shaggy

> ---
>   fs/jfs/jfs_txnmgr.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/jfs/jfs_txnmgr.c b/fs/jfs/jfs_txnmgr.c
> index be17e3c43582..7840a03e5bcb 100644
> --- a/fs/jfs/jfs_txnmgr.c
> +++ b/fs/jfs/jfs_txnmgr.c
> @@ -272,14 +272,15 @@ int txInit(void)
>   	if (TxBlock == NULL)
>   		return -ENOMEM;
>   
> -	for (k = 1; k < nTxBlock - 1; k++) {
> -		TxBlock[k].next = k + 1;
> +	for (k = 0; k < nTxBlock; k++) {
>   		init_waitqueue_head(&TxBlock[k].gcwait);
>   		init_waitqueue_head(&TxBlock[k].waitor);
>   	}
> +
> +	for (k = 1; k < nTxBlock - 1; k++) {
> +		TxBlock[k].next = k + 1;
> +	}
>   	TxBlock[k].next = 0;
> -	init_waitqueue_head(&TxBlock[k].gcwait);
> -	init_waitqueue_head(&TxBlock[k].waitor);
>   
>   	TxAnchor.freetid = 1;
>   	init_waitqueue_head(&TxAnchor.freewait);