Re: [syzbot] [mm?] WARNING: lock held when returning to user space in lock_next_vma

[Hillf Danton <hdanton@sina.com>]

> Date: Tue, 08 Jul 2025 10:52:27 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    26ffb3d6f02c Add linux-next specific files for 20250704
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1719df70580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1e4f88512ae53408
> dashboard link: https://syzkaller.appspot.com/bug?extid=80011ad33eec39e6ce42
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1124abd4580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1099df70580000

#syz test

--- x/fs/proc/task_mmu.c
+++ y/fs/proc/task_mmu.c
@@ -586,6 +586,7 @@ 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;
@@ -630,6 +631,7 @@ static int do_procmap_query(struct proc_
 		return -ENOMEM;
 	}
 
+	mutex_lock(&query_mutex);
 	err = query_vma_setup(priv);
 	if (err)
 		goto fail_vma_setup;
@@ -712,6 +714,7 @@ 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),
@@ -733,6 +736,7 @@ static int do_procmap_query(struct proc_
 out:
 	query_vma_teardown(priv);
 fail_vma_setup:
+	mutex_unlock(&query_mutex);
 	mmput(mm);
 	kfree(name_buf);
 	return err;
--