[Nouveau] [REGRESSION] nouveau: Crash in gk104_fifo_intr_runlist()

[Eric Biggers]

Hi,

I am testing Linux v4.2-rc5 and I am sporadically getting crashes shortly after
startup in gk104_fifo_intr_runlist().  What I've found is that the 'mask' value
read from offset 0x2a00 comes back as '0xbad0da00'.  This causes the 'engn'
variable to be assigned the value 9, which is invalid; then wake_up() is called
on an uninitialized waitqueue which causes the crash.

Reverting commit 1addc12648521d ("drm/nouveau/fifo/gk104: kick channels when
deactivating them") seemed to make the problem go away, although I can't be 100%
sure because the problem is sporadic.

Attached an example of the kernel log up to the crash.

Eric
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