BUG: unable to handle kernel NULL pointer dereference in sha1_mb_mgr_get_comp_job_avx2

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    a38523185b40 erge tag 'libnvdimm-fixes-4.19-rc6' of git://..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1767b7fa400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dfb440e26f0a6f6f
dashboard link: https://syzkaller.appspot.com/bug?extid=87dbe4b17debcec16d71
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+87dbe4b17debcec16d71@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: unable to handle kernel NULL pointer dereference at 0000000000000034
PGD 1b8b87067 P4D 1b8b87067 PUD 1b8b88067 PMD 0
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 24 Comm: kworker/1:1 Not tainted 4.19.0-rc5+ #32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: crypto mcryptd_flusher
RIP: 0010:sha1_mb_mgr_get_comp_job_avx2+0x62/0xba  
arch/x86/crypto/sha1-mb/sha1_mb_mgr_flush_avx2.S:256
Code: 04 c4 e2 69 3b d3 c4 c1 79 7e d0 49 f7 c0 f0 ff ff ff 75 6e 49 6b d8  
08 48 8d 9c 1f 08 01 00 00 48 8b 03 48 c7 03 00 00 00 00 <c7> 40 34 02 00  
00 00 48 8b 9f 00 01 00 00 48 c1 e3 04 4c 09 c3 48
kobject: 'loop1' (00000000307f8c2f): kobject_uevent_env
RSP: 0018:ffff8801d94473c0 EFLAGS: 00010206
RAX: 0000000000000000 RBX: ffff8801d4818688 RCX: 1ffff1003b2869e1
RDX: 1ffffd1ffffa2591 RSI: ffffffff81454f3a RDI: ffff8801d4818580
RBP: ffff8801d9447520 R08: 0000000000000000 R09: 0000000000000006
kobject: 'loop1' (00000000307f8c2f): fill_kobj_path: path  
= '/devices/virtual/block/loop1'
R10: 0000000000000000 R11: ffff8801d9434640 R12: ffff8801d94474f8
R13: 0000000000000001 R14: ffff8801bb509720 R15: 0000000000000200
FS:  0000000000000000(0000) GS:ffff8801dad00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
kobject: 'loop4' (00000000fa342cfc): kobject_uevent_env
CR2: 0000000000000034 CR3: 00000001b8b85000 CR4: 00000000001406e0
kobject: 'loop4' (00000000fa342cfc): fill_kobj_path: path  
= '/devices/virtual/block/loop4'
Call Trace:
 sha1_mb_flusher+0x2f4/0x60b arch/x86/crypto/sha1-mb/sha1_mb.c:918
 mcryptd_flusher+0x3af/0x520 crypto/mcryptd.c:208
 process_one_work+0xc90/0x1b90 kernel/workqueue.c:2153
 worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
 kthread+0x35a/0x420 kernel/kthread.c:246
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:413
Modules linked in:
CR2: 0000000000000034
---[ end trace 7d3a48e5625a9543 ]---
RIP: 0010:sha1_mb_mgr_get_comp_job_avx2+0x62/0xba  
arch/x86/crypto/sha1-mb/sha1_mb_mgr_flush_avx2.S:256
Code: 04 c4 e2 69 3b d3 c4 c1 79 7e d0 49 f7 c0 f0 ff ff ff 75 6e 49 6b d8  
08 48 8d 9c 1f 08 01 00 00 48 8b 03 48 c7 03 00 00 00 00 <c7> 40 34 02 00  
00 00 48 8b 9f 00 01 00 00 48 c1 e3 04 4c 09 c3 48
RSP: 0018:ffff8801d94473c0 EFLAGS: 00010206
RAX: 0000000000000000 RBX: ffff8801d4818688 RCX: 1ffff1003b2869e1
RDX: 1ffffd1ffffa2591 RSI: ffffffff81454f3a RDI: ffff8801d4818580
RBP: ffff8801d9447520 R08: 0000000000000000 R09: 0000000000000006
R10: 0000000000000000 R11: ffff8801d9434640 R12: ffff8801d94474f8
R13: 0000000000000001 R14: ffff8801bb509720 R15: 0000000000000200
FS:  0000000000000000(0000) GS:ffff8801dad00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000034 CR3: 00000001b8b85000 CR4: 00000000001406e0


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