BUG: kernel NULL pointer dereference, address: 0000000000000080
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 213996067 P4D 213996067 PUD 212456067 PMD 0 
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 3523 Comm: kworker/u4:5 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
RIP: 0010:qlink_to_object mm/kasan/quarantine.c:137 [inline]
RIP: 0010:qlink_free mm/kasan/quarantine.c:142 [inline]
RIP: 0010:qlist_free_all+0x36/0x170 mm/kasan/quarantine.c:168
Code: 53 48 83 ec 10 48 8b 37 48 85 f6 0f 84 36 01 00 00 49 bf 00 00 00 00 00 fc ff df 48 85 ed 49 89 fd 48 89 ef 0f 84 97 00 00 00 <48> 63 87 80 00 00 00 4c 8b 26 48 29 c6 48 83 3d 95 60 25 08 00 0f
RSP: 0018:ffffc900053d72a8 EFLAGS: 00010246
RAX: ffffea0000000000 RBX: 0000000000000286 RCX: ffffea0000000007
RDX: 0000000000000000 RSI: ffff888000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000001 R09: ffffffff8ce2da8f
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888000000000
R13: ffffc900053d72f0 R14: 0000000000000200 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 000000020ec3b000 CR4: 00000000001526e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 quarantine_reduce+0x17e/0x200 mm/kasan/quarantine.c:261
 __kasan_kmalloc.constprop.0+0x9e/0xd0 mm/kasan/common.c:442
 slab_post_alloc_hook mm/slab.h:518 [inline]
 slab_alloc mm/slab.c:3312 [inline]
 kmem_cache_alloc+0x13a/0x3f0 mm/slab.c:3482
 kmem_cache_zalloc include/linux/slab.h:656 [inline]
 ext4_init_io_end+0x23/0x170 fs/ext4/page-io.c:279
 ext4_writepages+0x8e4/0x3990 fs/ext4/inode.c:2730
 do_writepages+0xec/0x290 mm/page-writeback.c:2352
 __writeback_single_inode+0x125/0x1400 fs/fs-writeback.c:1461
 writeback_sb_inodes+0x53d/0xf40 fs/fs-writeback.c:1721
 __writeback_inodes_wb+0xc6/0x280 fs/fs-writeback.c:1790
 wb_writeback+0x8bb/0xd40 fs/fs-writeback.c:1896
 wb_check_old_data_flush fs/fs-writeback.c:1998 [inline]
 wb_do_writeback fs/fs-writeback.c:2051 [inline]
 wb_workfn+0x8f5/0x13e0 fs/fs-writeback.c:2080
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Modules linked in:
CR2: 0000000000000080
---[ end trace 567c9364aaa5a5cf ]---
RIP: 0010:qlink_to_object mm/kasan/quarantine.c:137 [inline]
RIP: 0010:qlink_free mm/kasan/quarantine.c:142 [inline]
RIP: 0010:qlist_free_all+0x36/0x170 mm/kasan/quarantine.c:168
Code: 53 48 83 ec 10 48 8b 37 48 85 f6 0f 84 36 01 00 00 49 bf 00 00 00 00 00 fc ff df 48 85 ed 49 89 fd 48 89 ef 0f 84 97 00 00 00 <48> 63 87 80 00 00 00 4c 8b 26 48 29 c6 48 83 3d 95 60 25 08 00 0f
RSP: 0018:ffffc900053d72a8 EFLAGS: 00010246
RAX: ffffea0000000000 RBX: 0000000000000286 RCX: ffffea0000000007
RDX: 0000000000000000 RSI: ffff888000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000001 R09: ffffffff8ce2da8f
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888000000000
R13: ffffc900053d72f0 R14: 0000000000000200 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 000000020ec3b000 CR4: 00000000001526e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400