Hello,
FYI this happens in mainline kernel 4.14.0-00902-g43ff2f4.
It looks happen since 4.11.
It occurs in 12 out of 108 boots.
[ 20.057810] ata2: PATA max MWDMA2 cmd 0x170 ctl 0x376 bmdma 0xc0c8 irq 15
[ 20.219346] ata2.01: NODEV after polling detection
[ 20.222140] ata2.00: ATAPI: QEMU DVD-ROM, 2.5+, max UDMA/100
[ 20.232461] ata2.00: configured for MWDMA2
[ 20.235209] ata2.00: disabled
[ 20.247746] BUG: unable to handle kernel NULL pointer dereference at 0000000000000350
[ 20.250638] IP: ata_port_wait_eh+0xa1/0xe5:
ata_port_wait_eh at include/scsi/scsi_host.h:764
[ 20.251018] PGD 0 P4D 0
[ 20.251018] Oops: 0000 [#1] PREEMPT SMP
[ 20.255428] CPU: 1 PID: 5 Comm: kworker/u4:0 Not tainted 4.14.0-00902-g43ff2f4 #1
[ 20.255428] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[ 20.263368] scsi host0: ata_piix
[ 20.267396] Workqueue: events_unbound async_run_entry_fn
[ 20.270725] scsi host1: ata_piix
[ 20.271036] ata3: PATA max MWDMA2 cmd 0x1f0 ctl 0x3f6 bmdma 0xc0c0 irq 14
[ 20.271039] ata4: PATA max MWDMA2 cmd 0x170 ctl 0x376 bmdma 0xc0c8 irq 15
[ 20.283654] Rounding down aligned max_sectors from 4294967295 to 4294967288
[ 20.298430] task: ffff8800001e6140 task.stack: ffff8800001e8000
[ 20.298430] RIP: 0010:ata_port_wait_eh+0xa1/0xe5:
ata_port_wait_eh at include/scsi/scsi_host.h:764
[ 20.298430] RSP: 0000:ffff8800001ebdc0 EFLAGS: 00010286
[ 20.304162] mtdoops: mtd device (mtddev=name/number) must be supplied
[ 20.304484] platform physmap-flash.0: failed to claim resource 0: [mem 0x08000000-0x07ffffff]
[ 20.305254] slram: not enough parameters.
[ 20.305257] Ramix PMC551 PCI Mezzanine Ram Driver. (C) 1999,2000 Nortel Networks.
[ 20.305263] pmc551: not detected
[ 20.327390] RAX: ffffffffffffffff RBX: ffff8800198a8000 RCX: ffff88001c80d8c0
[ 20.327390] RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000246
[ 20.327390] RBP: 0000000000000246 R08: 0000000845a00e34 R09: 0000000000000000
[ 20.337395] R10: ffffffff95122ad0 R11: 0000000000000105 R12: ffff8800198ac008
[ 20.337395] R13: ffff880000081000 R14: 0000000000000000 R15: 0000000000000000
[ 20.347394] FS: 0000000000000000(0000) GS:ffff88001c800000(0000) knlGS:0000000000000000
[ 20.347394] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 20.357398] CR2: 0000000000000350 CR3: 000000001dc69000 CR4: 00000000000006a0
[ 20.357398] Call Trace:
[ 20.357398] ? __list_del_entry+0x1d/0x1d:
rcu_read_unlock at include/linux/rcupdate.h:686
__list_del_entry+0x1d/0x1d:
copy_siginfo at include/linux/signal.h:16
__list_del_entry+0x1d/0x1d:
worker_detach_from_pool at kernel/workqueue.c:1727
__list_del_entry+0x1d/0x1d:
kthread at kernel/kthread.c:190
__list_del_entry+0x1d/0x1d:
attach_task at kernel/sched/fair.c:7239
__list_del_entry+0x1d/0x1d:
rt_se_prio at kernel/sched/rt.c:891
__list_del_entry+0x1d/0x1d:
autoremove_wake_function at kernel/sched/wait.c:376
[ 20.357398] ata_port_probe+0x24/0x28:
ata_port_probe at drivers/ata/libata-core.c:6395
[ 20.367393] async_port_probe+0x2b/0x42:
async_port_probe at drivers/ata/libata-core.c:6415
[ 20.367393] async_run_entry_fn+0x35/0x105:
async_run_entry_fn at kernel/async.c:124
[ 20.367393] process_one_work+0x1c9/0x310: