dmaengine: pl330 rare NULL pointer dereference in pl330_tasklet

[Krzysztof Kozlowski]

Hi all,

I hit quite rare issue with pl330 DMA driver, difficult to reproduce
(actually failed to do so):

Happened during early reboot

[  OK  ] Stopped target Graphical Interface.
[  OK  ] Stopped target Multi-User System.
[  OK  ] Stopped target RPC Port Mapper.
         Stopping OpenSSH Daemonti[   75.447904] 8<--- cut here ---
[   75.449506] Unable to handle kernel NULL pointer dereference at virtual address 0000000c
...
[   75.690850] [<c0902f70>] (pl330_tasklet) from [<c034d460>] (tasklet_action_common+0x88/0x1f4)
[   75.699340] [<c034d460>] (tasklet_action_common) from [<c03013f8>] (__do_softirq+0x108/0x428)
[   75.707850] [<c03013f8>] (__do_softirq) from [<c034dadc>] (run_ksoftirqd+0x2c/0x4c)
[   75.715486] [<c034dadc>] (run_ksoftirqd) from [<c036fbfc>] (smpboot_thread_fn+0x13c/0x24c)
[   75.723693] [<c036fbfc>] (smpboot_thread_fn) from [<c036c18c>] (kthread+0x13c/0x16c)
[   75.731390] [<c036c18c>] (kthread) from [<c03001a8>] (ret_from_fork+0x14/0x2c)

Full log:
https://krzk.eu/#/builders/20/builds/954/steps/22/logs/serial0

1. Arch ARM Linux
2. multi_v7_defconfig
3. Odroid HC1, ARMv7, octa-core (Cortex-A7+A15), Exynos5422 SoC
4. systemd, boot up with static IP set in kernel command line
5. No swap
6. Kernel, DTB and initramfs are downloaded with TFTP
7. NFS root (NFS client) mounted from a NFSv4 server

Since I was not able to reproduce it, obviously I did not run bisect. If
anyone has ideas, please share.

Best regards,
Krzysztof