On Tue, Nov 21, 2017 at 1:19 PM, Fengguang Wu [off-list ref] wrote:

On Tue, Nov 21, 2017 at 08:09:35PM +0800, Fengguang Wu wrote:

quoted

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:

Here is a similar issue in ata_scsi_scan_host(). It only happened once.


/pkg/linux/x86_64-randconfig-in0-11110243/gcc-6/cf9b0772f2e410645fece13b749bd56505b998b8/dmesg-vm-ivb41-quantal-x86_64-4:20171120120806:x86_64-randconfig-in0-11110243:4.14.0-10859-gcf9b077:1

[   56.376960] ata2.00: ATAPI: QEMU DVD-ROM, 2.5+, max UDMA/100
[   56.379169] ata2.00: configured for MWDMA2
[   56.381518] ata2.00: disabled
[   56.385696] sd 1:0:0:0: [sda] Attached SCSI disk
[   56.395326] sd 1:0:0:0: [sda] Synchronizing SCSI cache

I guess both can be explained by the same race as the previous one, with
async probe racing against removal. The first one might be a use-after-free
problem, the second one could be the probing thread running after the
device got removed.

           Arnd