BUG: unable to handle kernel NULL pointer dereference in loop_rw_iter

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    9420f1ce Merge tag 'pinctrl-v5.9-1' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13662f62900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=72cf85e4237850c8
dashboard link: https://syzkaller.appspot.com/bug?extid=1abbd16e49910f6bbe45
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15929006900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15e196aa900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1abbd16e49910f6bbe45@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD a652e067 P4D a652e067 PUD a652f067 PMD 0 
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 7461 Comm: io_wqe_worker-0 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:0x0
Code: Bad RIP value.
RSP: 0018:ffffc9000804f910 EFLAGS: 00010246
RAX: 1ffffffff10b0b9b RBX: dffffc0000000000 RCX: ffff88808962e1c8
RDX: 000000000000003c RSI: 0000000020000740 RDI: ffff88809fb2dcc0
RBP: 0000000020000740 R08: ffffc9000804fa28 R09: ffff8880a7639c0f
R10: 0000000000000000 R11: 0000000000000000 R12: ffffc9000804fa28
R13: ffffffff88585cc0 R14: 000000000000003c R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000008e2a7000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 loop_rw_iter.part.0+0x26e/0x450 fs/io_uring.c:2850
 loop_rw_iter fs/io_uring.c:2829 [inline]
 io_write+0x6a2/0x7a0 fs/io_uring.c:3190
 io_issue_sqe+0x1b0/0x60d0 fs/io_uring.c:5530
 io_wq_submit_work+0x183/0x3d0 fs/io_uring.c:5775
 io_worker_handle_work+0xa45/0x13f0 fs/io-wq.c:527
 io_wqe_worker+0xbf0/0x10e0 fs/io-wq.c:569
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Modules linked in:
CR2: 0000000000000000
---[ end trace 97e511c5a98da2fe ]---
RIP: 0010:0x0
Code: Bad RIP value.
RSP: 0018:ffffc9000804f910 EFLAGS: 00010246
RAX: 1ffffffff10b0b9b RBX: dffffc0000000000 RCX: ffff88808962e1c8
RDX: 000000000000003c RSI: 0000000020000740 RDI: ffff88809fb2dcc0
RBP: 0000000020000740 R08: ffffc9000804fa28 R09: ffff8880a7639c0f
R10: 0000000000000000 R11: 0000000000000000 R12: ffffc9000804fa28
R13: ffffffff88585cc0 R14: 000000000000003c R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f84c3b15028 CR3: 000000008e2a7000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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