[syzbot] [fs?] general protection fault in iter_file_splice_write

[syzbot]

syzbot has bisected this issue to:

commit 2df86547b23dabcd02ab000a24ed7813606c269f
Author: David Howells <dhowells at redhat.com>
Date:   Fri Mar 8 12:36:05 2024 +0000

    netfs: Cut over to using new writeback code

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=148b014b980000
start commit:   5189dafa4cf9 Merge tag 'nfsd-6.11-1' of git://git.kernel.o..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=168b014b980000
console output: https://syzkaller.appspot.com/x/log.txt?x=128b014b980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e8a2eef9745ade09
dashboard link: https://syzkaller.appspot.com/bug?extid=d2125fcb6aa8c4276fd2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16828c5d980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=103c7805980000

Reported-by: syzbot+d2125fcb6aa8c4276fd2 at syzkaller.appspotmail.com
Fixes: 2df86547b23d ("netfs: Cut over to using new writeback code")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection