Re: [syzbot] [fs?] BUG: unable to handle kernel paging request in mmu_notifier_invalidate_range_start

[Hillf Danton]

On Fri, 29 Dec 2023 11:44:19 -0800
> HEAD commit:    aafe7ad77b91 Merge branch 'for-next/core' into for-kernelci
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12ef73d6e80000

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

--- x/fs/proc/task_mmu.c
+++ y/fs/proc/task_mmu.c
@@ -2491,8 +2491,9 @@ static long do_pagemap_cmd(struct file *
 
 	switch (cmd) {
 	case PAGEMAP_SCAN:
-		return do_pagemap_scan(mm, arg);
-
+		if (mm)
+			return do_pagemap_scan(mm, arg);
+		/* fall thru */
 	default:
 		return -EINVAL;
 	}
--