ibmvstgt/aio broken with 2.6.20-rc6 powerpc

[Bastian Blank <bastian@waldi.eu.org>]

Hi folks

I'm not really sure if this is a ibmvstgt or a generic aio problem.

I tried ibmvstgt on my openpower and the kernel shows the following
warning several times:
| Jan 28 15:11:15 waldi kernel: Badness at arch/powerpc/mm/slb.c:95
| Jan 28 15:11:15 waldi kernel: Call Trace:
| Jan 28 15:11:15 waldi kernel: [C00000000282B750] [C00000000000EC94] .show_stack+0x68/0x1b0 (unreliable)
| Jan 28 15:11:15 waldi kernel: [C00000000282B7F0] [C00000000015ED64] .report_bug+0x94/0xe8
| Jan 28 15:11:15 waldi kernel: [C00000000282B880] [C0000000000228DC] .program_check_exception+0x140/0x54c
| Jan 28 15:11:15 waldi kernel: [C00000000282B920] [C000000000004774] program_check_common+0xf4/0x100
| Jan 28 15:11:15 waldi kernel: --- Exception: 700 at .slb_flush_and_rebolt+0xc/0xe0
| Jan 28 15:11:15 waldi kernel:     LR = .switch_slb+0xac/0x1a0
| Jan 28 15:11:15 waldi kernel: [C00000000282BC10] [FFFFFFFFFFFFFFFF] 0xffffffffffffffff (unreliable)
| Jan 28 15:11:15 waldi kernel: [C00000000282BCB0] [C0000000000E1750] .aio_kick_handler+0x128/0x278
| Jan 28 15:11:15 waldi kernel: [C00000000282BD60] [C000000000066380] .run_workqueue+0xec/0x1d4
| Jan 28 15:11:15 waldi kernel: [C00000000282BE00] [C000000000066F2C] .worker_thread+0x164/0x1bc
| Jan 28 15:11:15 waldi kernel: [C00000000282BEE0] [C00000000006B6E8] .kthread+0x120/0x170
| Jan 28 15:11:15 waldi kernel: [C00000000282BF90] [C000000000024204] .kernel_thread+0x4c/0x68

One possibility:
aio_kick_handler calls use_mm. use_mm calls switch_mm. It seems that
90aef12e6dd609e1ad7fb70044eedc78ca55ee5e changed that from activate_mm.

activate_mm on powerpc disables interupts and calls swtich_mm. So
switch_mm is now called with interrupts enabled and runs into the
WARN_ON.

Bastian

-- 
She won' go Warp 7, Cap'n!  The batteries are dead!
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