jfs: fix corrupted list in dbUpdatePMap

This patch resolves the "list_add corruption. next is NULL" Oops
reported by syzkaller in dbUpdatePMap(). The root cause is uninitialized
synclist nodes in struct metapage and struct TxBlock, plus improper list
node removal using list_del() (which leaves nodes in an invalid state).

This fixes the following Oops reported by syzkaller.

list_add corruption. next is NULL.
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:28!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 122 Comm: jfsCommit Not tainted syzkaller #0
PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 10/02/2025
RIP: 0010:__list_add_valid_or_report+0xc3/0x130 lib/list_debug.c:27
Code: 4c 89 f2 48 89 d9 e8 0c 88 a4 fc 90 0f 0b 48 c7 c7 20 de 3d 8b e8
fd 87 a4 fc 90 0f 0b 48 c7 c7 c0 de 3d 8b e8 ee 87 a4 fc 90 <0f> 0b 48
89 df e8 13 c3 7d fd 42 80 7c 2d 00 00 74 08 4c 89 e7 e8
RSP: 0018:ffffc9000395fa20 EFLAGS: 00010246
RAX: 0000000000000022 RBX: 0000000000000000 RCX: 270c5dfadb559700
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00000000000f0000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff5200072bee9 R12: 0000000000000000
R13: dffffc0000000000 R14: 0000000000000004 R15: 1ffff92000632266
FS:  0000000000000000(0000) GS:ffff888126ef9000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056341fdb86c0 CR3: 0000000040a18000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __list_add_valid include/linux/list.h:96 [inline]
 __list_add include/linux/list.h:158 [inline]
 list_add include/linux/list.h:177 [inline]
 dbUpdatePMap+0x7e4/0xeb0 fs/jfs/jfs_dmap.c:577
 txAllocPMap+0x57d/0x6b0 fs/jfs/jfs_txnmgr.c:2426
 txUpdateMap+0x81e/0x9c0 fs/jfs/jfs_txnmgr.c:2364
 txLazyCommit fs/jfs/jfs_txnmgr.c:2665 [inline]
 jfs_lazycommit+0x3f1/0xa10 fs/jfs/jfs_txnmgr.c:2734
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---

Reported-by: syzbot+4d0a0feb49c5138cac46@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4d0a0feb49c5138cac46
Tested-by: syzbot+4d0a0feb49c5138cac46@syzkaller.appspotmail.com
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

Author: zhouyun1306

fs/jfs/jfs_metapage.c

@@ -270,6 +270,7 @@ static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
 		mp->clsn = 0;
 		mp->log = NULL;
 		init_waitqueue_head(&mp->wait);
+		INIT_LIST_HEAD(&mp->synclist);
 	}
 	return mp;
 }
@@ -379,7 +380,7 @@ static void remove_from_logsync(struct metapage *mp)
 		mp->lsn = 0;
 		mp->clsn = 0;
 		log->count--;
-		list_del(&mp->synclist);
+		list_del_init(&mp->synclist);
 	}
 	LOGSYNC_UNLOCK(log, flags);
 }

fs/jfs/jfs_txnmgr.c

@@ -275,6 +275,7 @@ int txInit(void)
 	for (k = 0; k < nTxBlock; k++) {
 		init_waitqueue_head(&TxBlock[k].gcwait);
 		init_waitqueue_head(&TxBlock[k].waitor);
+		INIT_LIST_HEAD(&TxBlock[k].synclist);
 	}
 
 	for (k = 1; k < nTxBlock - 1; k++) {
@@ -974,7 +975,7 @@ static void txUnlock(struct tblock * tblk)
 	if (tblk->lsn) {
 		LOGSYNC_LOCK(log, flags);
 		log->count--;
-		list_del(&tblk->synclist);
+		list_del_init(&tblk->synclist);
 		LOGSYNC_UNLOCK(log, flags);
 	}
 }