Hi, I upgraded from 5.11.17 to 5.13.2 kernel few days ago. Today I got this bug: ``` BUG: kernel NULL pointer dereference, address: 00000000000000d8 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] SMP PTI CPU: 21 PID: 6427 Comm: kworker/21:1H Not tainted 5.13.2 #1 Hardware name: Dell Inc. PowerEdge R720/0020HJ, BIOS 2.9.0 12/06/2019 Workqueue: kblockd blk_mq_timeout_work RIP: 0010:blk_mq_put_rq_ref+0xd/0x4b Code: 44 24 07 48 8b 4c 24 08 65 48 2b 0c 25 28 00 00 00 74 05 e8 79 65 9e 00 48 83 c4 10 c3 0f 1f 44 00 00 55 48 8b 47 10 48 89 fd <48> 8b 80 d8 00 00 00 48 3b 78 40 75 0f 48 8b 87 00 01 00 00 31 f6 RSP: 0018:ffffb1dd98b07d80 EFLAGS: 00010206 RAX: 0000000000000000 RBX: ffffb1dd98b07e10 RCX: ffff89a55330adc0 RDX: 0000000000000001 RSI: 0000000000000202 RDI: ffff89bcc1432400 RBP: ffff89bcc1432400 R08: 0000000000000000 R09: 0000000000000000 R10: 000000000000000b R11: fefefefefefefeff R12: 00000000000003e4 R13: ffff89bcc1bbd000 R14: ffffb1dd98b07e00 R15: ffff89a54dea0118 FS: 0000000000000000(0000) GS:ffff89d45fa80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000000000d8 CR3: 000000270be0c002 CR4: 00000000001726e0 Call Trace: bt_iter+0x6a/0x76 __sbitmap_for_each_set.constprop.0+0xa4/0xe2 ? bt_tags_iter+0x8a/0x8a ``` Following this bug, the server disk activity stopped and I had to hard reboot the server. I have found this patch, not published yet, that could be related but not sure at all: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b407bf68af325786b5f572a5e38d51206914f91b