2.6.19-rc1: Oops in probe_hwif

[Brent Casavant <bcasavan@sgi.com>]

While working on a patch to remove the SN dependencies from the
ioc4 driver, I ran across the included oops in the IDE code.

I believe the problem is that HWIF(drive) is NULL in SELECT_DRIVE.
This seems to be confirmed by the value of r10 in the oops output,
which contains &(HWIF(drive)->intrproc) at the moment of the oops.

If my reading of the IDE code is correct (I'm no expert, to be sure),
the "hwif" field of an ide_drive_t is initialized in init_irq() in
ide-probe.c.  However, this code has not been called yet.  The structure
of function calls as-coded is:

	probe_hwif_init_with_fixup
		probe_hwif
			wait_hwif_ready
				SELECT_DRIVE
		hwif_init
			init_irq

So, unless I'm missing something, there seems to be a use of an
(ide_drive_t*)->hwif field (in SELECT_DRIVE()) before it is initialized
(in init_irq()).

Thanks,
Brent Casavant

Unable to handle kernel NULL pointer dereference (address 0000000000000840)
swapper[1]: Oops 8813272891392 [1]
Modules linked in:

Pid: 1, CPU 0, comm:              swapper
psr : 00001010085a6010 ifs : 8000000000000287 ip  : [<a0000001005262d0>]    Not tainted
ip is at SELECT_DRIVE+0x30/0xe0
unat: 0000000000000000 pfs : 000000000000040a rsc : 0000000000000003
rnat: 9ffffffff6000000 bsps: 000000000000fffe pr  : 000000000000a581
ldrs: 0000000000000000 ccv : 0000000000000000 fpsr: 0009804c8a70433f
csd : 0000000000000000 ssd : 0000000000000000
b0  : a00000010052c670 b6  : a00000010051bec0 b7  : a0000001004cbe40
f6  : 1003e0000000138800000 f7  : 1003e431bde82d7b634db
f8  : 1003e0000000001312d00 f9  : 1003e00000004a817c800
f10 : 1003e00000000000003e8 f11 : 1003e0000000000000000
r1  : a000000100eb6ef0 r2  : a000000100ccfae8 r3  : a000000100ccfae8
r8  : 0000000000000000 r9  : 0000000000000000 r10 : 0000000000000840
r11 : 0000000000000000 r12 : e00000307a6c7d20 r13 : e00000307a6c0000
r14 : 00000000000000ff r15 : 0000000000000050 r16 : 0000000000000000
r17 : e00000307a279398 r18 : 0000000000000000 r19 : 0000000000000020
r20 : e000003003110000 r21 : 0000000000000000 r22 : 0000000000000000
r23 : 000000000000000f r24 : e00000307a3da480 r25 : ffffffffffff4230
r26 : e0000030030a4000 r27 : 0000000000000000 r28 : e00000307a279390
r29 : e00000307a279380 r30 : 0000000000000000 r31 : e000003003105238

Call Trace:
 [<a0000001000129c0>] show_stack+0x40/0xa0
                                sp=e00000307a6c78d0 bsp=e00000307a6c0fe0
 [<a0000001000132c0>] show_regs+0x840/0x880
                                sp=e00000307a6c7aa0 bsp=e00000307a6c0f88
 [<a000000100034c90>] die+0x250/0x320
                                sp=e00000307a6c7aa0 bsp=e00000307a6c0f40
 [<a000000100058990>] ia64_do_page_fault+0x930/0xa60
                                sp=e00000307a6c7ac0 bsp=e00000307a6c0ef0
 [<a00000010000bb40>] ia64_leave_kernel+0x0/0x290
                                sp=e00000307a6c7b50 bsp=e00000307a6c0ef0
 [<a0000001005262d0>] SELECT_DRIVE+0x30/0xe0
                                sp=e00000307a6c7d20 bsp=e00000307a6c0eb8
 [<a00000010052c670>] wait_hwif_ready+0x90/0x1a0
                                sp=e00000307a6c7d20 bsp=e00000307a6c0e78
 [<a00000010052e130>] probe_hwif+0x1f0/0x1020
                                sp=e00000307a6c7d20 bsp=e00000307a6c0e08
 [<a000000100530830>] probe_hwif_init_with_fixup+0x30/0x1a0
                                sp=e00000307a6c7d20 bsp=e00000307a6c0dd8
 [<a0000001005309d0>] probe_hwif_init+0x30/0x60
                                sp=e00000307a6c7d20 bsp=e00000307a6c0db8
 [<a00000010051be50>] ioc4_ide_attach_one+0x570/0x5e0
                                sp=e00000307a6c7d20 bsp=e00000307a6c0d58
 [<a0000001004ef990>] ioc4_register_submodule+0xd0/0x200
                                sp=e00000307a6c7d30 bsp=e00000307a6c0d30
 [<a00000010051a580>] ioc4_ide_init+0x20/0x40
                                sp=e00000307a6c7d30 bsp=e00000307a6c0d18
 [<a000000100009720>] init+0x420/0x840
                                sp=e00000307a6c7d30 bsp=e00000307a6c0ce8
 [<a000000100010f70>] kernel_thread_helper+0xd0/0x100
                                sp=e00000307a6c7e30 bsp=e00000307a6c0cc0
 [<a000000100009140>] start_kernel_thread+0x20/0x40
                                sp=e00000307a6c7e30 bsp=e00000307a6c0cc0
 <0>Kernel panic - not syncing: Attempted to kill init!


-- 
Brent Casavant                          All music is folk music.  I ain't
bcasavan@sgi.com                        never heard a horse sing a song.
Silicon Graphics, Inc.                    -- Louis Armstrong