new smi_reader / smi_writer issues Code: bad PC value

[great9]

Great work getting these separated and into trackable threads.

There's an issue which could be reproduced by unloading the smi_stream_dev module.
I get:

Message from syslogd@localhost at Jan 12 09:39:38 ...
 kernel:[160197.085869] Internal error: Oops: 86000007 [#7] PREEMPT SMP

Message from syslogd@localhost at Jan 12 09:39:38 ...
 kernel:[160197.207909] Code: bad PC value

Message from syslogd@localhost at Jan 12 09:39:38 ...
 kernel:[160197.211592] Internal error: Oops: 86000007 [#8] PREEMPT SMP

Message from syslogd@localhost at Jan 12 09:39:38 ...
 kernel:[160197.317698] Code: bad PC value

[160190.582343] smi-stream-dev: error rx kfifo_alloc
[160190.794167] smi-stream-dev: error rx kfifo_alloc
[160196.996857] smi-stream-dev soc:smi_dev: smi-stream-dev: smi-stream dev removed
[160197.032815] Unable to handle kernel paging request at virtual address ffffc23694ee68c0
[160197.032838] Unable to handle kernel paging request at virtual address ffffc23694ee6b64
[160197.040485] Mem abort info:
[160197.048924] Mem abort info:
[160197.051146]   ESR = 0x86000007
[160197.053998]   ESR = 0x86000007
[160197.057505]   EC = 0x21: IABT (current EL), IL = 32 bits
[160197.060263]   EC = 0x21: IABT (current EL), IL = 32 bits
[160197.063371]   SET = 0, FnV = 0
[160197.066092]   SET = 0, FnV = 0
[160197.071233]   EA = 0, S1PTW = 0
[160197.071846]   EA = 0, S1PTW = 0
[160197.073939] swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000001243000
[160197.076632] swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000001243000
[160197.078782] [ffffc23694ee6b64] pgd=00000000373ff003, pud=00000000347e3003, pmd=00000000335b6003, pte=0000000000000000
[160197.081288] [ffffc23694ee68c0] pgd=00000000373ff003, pud=00000000347e3003, pmd=00000000335b6003, pte=0000000000000000
[160197.085869] Internal error: Oops: 86000007 [#7] PREEMPT SMP
[160197.085877] Modules linked in: bcm2835_smi aufs overlay dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua binfmt_misc brcmfmac brcmutil cfg80211 bcm2835_v4l2(CE) bcm2835_codec(CE) bcm2835_isp(CE) raspberrypi_hwmon v4l2_mem2mem bcm2835_mmal_vchiq(CE) videobuf2_vmalloc videobuf2_dma_contig videobuf2_memops videobuf2_v4l2 videobuf2_common videodev mc vc_sm_cma(CE) uio_pdrv_genirq uio sch_fq_codel drm ramoops reed_solomon ip_tables x_tables autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor xor_neon raid6_pq libcrc32c raid1 raid0 multipath linear spidev crct10dif_ce i2c_mux_pinctrl i2c_mux spi_bcm2835aux phy_generic aes_neon_bs aes_neon_blk crypto_simd cryptd [last unloaded: smi_stream_dev]
[160197.124859] CPU: 3 PID: 320736 Comm: smi-writer-thre Tainted: G      D  C OE     5.4.0-1100-raspi #112-Ubuntu
[160197.131987] Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
[160197.135708] pstate: 60400005 (nZCv daif +PAN -UAO)
[160197.139514] pc : 0xffffc23694ee6b64
[160197.143268] lr : 0xffffc23694ee6b64
[160197.147026] sp : ffff80001420be20
[160197.150781] x29: ffff80001420be20 x28: 0000000000000000 
[160197.154660] x27: ffff8000140939b8 x26: ffff0f76eee66ab8 
[160197.158463] x25: ffffc236fc4b2ca0 x24: ffffc23694ee6ae8 
[160197.162325] x23: ffffc23694ee8b58 x22: ffffc23694eeb000 
[160197.166096] x21: ffffc23694eeb000 x20: ffff0f76f1779f18 
[160197.169742] x19: ffffc23694eeb540 x18: 0000000000000000 
[160197.173268] x17: 0000000000000000 x16: 0000000000000000 
[160197.176669] x15: 0000000000000000 x14: 0000000000000000 
[160197.179945] x13: 0000000000000000 x12: 0000000000000000 
[160197.183086] x11: 0000000000000000 x10: 00000000000019d0 
[160197.186073] x9 : ffff80001420bc90 x8 : ffff0f76f51f1a30 
[160197.188977] x7 : 0000000000000000 x6 : 0000000000000000 
[160197.191776] x5 : ffffc236fcc0a000 x4 : ffff80001420c000 
[160197.194468] x3 : ffffc236fcc0a178 x2 : 0000000000000000 
[160197.197027] x1 : 0000000000000000 x0 : 0000000000000000 
[160197.199456] Call trace:
[160197.201730]  0xffffc23694ee6b64
[160197.203905]  kthread+0x150/0x170
[160197.205950]  ret_from_fork+0x10/0x1c
[160197.207909] Code: bad PC value
[160197.209754] ---[ end trace 366eecd13fc7e46f ]---
[160197.211592] Internal error: Oops: 86000007 [#8] PREEMPT SMP
[160197.213488] Modules linked in: bcm2835_smi aufs overlay dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua binfmt_misc brcmfmac brcmutil cfg80211 bcm2835_v4l2(CE) bcm2835_codec(CE) bcm2835_isp(CE) raspberrypi_hwmon v4l2_mem2mem bcm2835_mmal_vchiq(CE) videobuf2_vmalloc videobuf2_dma_contig videobuf2_memops videobuf2_v4l2 videobuf2_common videodev mc vc_sm_cma(CE) uio_pdrv_genirq uio sch_fq_codel drm ramoops reed_solomon ip_tables x_tables autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor xor_neon raid6_pq libcrc32c raid1 raid0 multipath linear spidev crct10dif_ce i2c_mux_pinctrl i2c_mux spi_bcm2835aux phy_generic aes_neon_bs aes_neon_blk crypto_simd cryptd [last unloaded: smi_stream_dev]
[160197.238680] CPU: 0 PID: 320735 Comm: smi-reader-thre Tainted: G      D  C OE     5.4.0-1100-raspi #112-Ubuntu
[160197.245141] Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
[160197.248596] pstate: 60400005 (nZCv daif +PAN -UAO)
[160197.252067] pc : 0xffffc23694ee68c0
[160197.255512] lr : 0xffffc23694ee68c0
[160197.258893] sp : ffff800014203e00
[160197.262273] x29: ffff800014203e00 x28: 0000000000000000 
[160197.265729] x27: ffff8000140939b8 x26: 0000000000000001 
[160197.269115] x25: ffffc23694ee8a48 x24: ffffc23694ee8aa8 
[160197.272521] x23: ffff0f76f51f5a00 x22: 0000000000080000 
[160197.275955] x21: 0000000000000001 x20: 0000000000000001 
[160197.279392] x19: ffffc23694eeb000 x18: 0000000000000000 
[160197.282824] x17: 0000000000000000 x16: 0000000000000000 
[160197.286214] x15: 0000000000000000 x14: 0000000000000000 
[160197.289503] x13: 0000000000000000 x12: 0000000000100000 
[160197.292656] x11: 0000000000000001 x10: 00000000000019d0 
[160197.295660] x9 : ffff800014203c70 x8 : ffff0f76f51f7430 
[160197.298582] x7 : 0000000000000000 x6 : 0000000000000000 
[160197.301401] x5 : ffffc236fcc0a000 x4 : ffff800014204000 
[160197.304119] x3 : ffffc236fcc0a178 x2 : 0000000000000000 
[160197.306704] x1 : 0000000000000000 x0 : 0000000000000000 
[160197.309159] Call trace:
[160197.311454]  0xffffc23694ee68c0
[160197.313647]  kthread+0x150/0x170
[160197.315715]  ret_from_fork+0x10/0x1c
[160197.317698] Code: bad PC value
[160197.319567] ---[ end trace 366eecd13fc7e470 ]---