Re: [syzbot] [fs?] WARNING: bad unlock balance in query_matching_vma

[Hillf Danton <hdanton@sina.com>]

> Date: Mon, 14 Jul 2025 14:11:36 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    a62b7a37e6fc Add linux-next specific files for 20250711
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1422dd82580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=7d42120e19faaef
> dashboard link: https://syzkaller.appspot.com/bug?extid=d4316c39e84f412115c9
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1222dd82580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1205d0f0580000

#syz test

--- x/fs/proc/task_mmu.c
+++ y/fs/proc/task_mmu.c
@@ -585,6 +585,7 @@ no_vma:
 	return ERR_PTR(-ENOENT);
 }
 
+static DEFINE_MUTEX(query_mutex);
 static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
 {
 	struct procmap_query karg;
@@ -620,8 +621,10 @@ static int do_procmap_query(struct proc_
 	if (!mm || !mmget_not_zero(mm))
 		return -ESRCH;
 
+	mutex_lock(&query_mutex);
 	err = query_vma_setup(priv);
 	if (err) {
+		mutex_unlock(&query_mutex);
 		mmput(mm);
 		return err;
 	}
@@ -712,6 +715,7 @@ static int do_procmap_query(struct proc_
 
 	/* unlock vma or mmap_lock, and put mm_struct before copying data to user */
 	query_vma_teardown(priv);
+	mutex_unlock(&query_mutex);
 	mmput(mm);
 
 	if (karg.vma_name_size && copy_to_user(u64_to_user_ptr(karg.vma_name_addr),
@@ -732,6 +736,7 @@ static int do_procmap_query(struct proc_
 
 out:
 	query_vma_teardown(priv);
+	mutex_unlock(&query_mutex);
 	mmput(mm);
 	kfree(name_buf);
 	return err;
--