Well, apparently not.
Flashing r17435-97e32e9702 causes router to be nonfunctional.
The following pstore items are then visible in recovery.
root@OpenWrt:~# cat /sys/fs/pstore/dmesg-ramoops-0
Oops#1 Part1
<5>[ 0.554467] 0x0000001c0000-0x0000002c0000 : "factory"
<5>[ 0.560941] 0x000000300000-0x000008000000 : "ubi"
<5>[ 0.594565] random: fast init done
<3>[ 0.696772] blk_update_request: I/O error, dev mtdblock2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
<3>[ 0.707136] Buffer I/O error on dev mtdblock2, logical block 0, async page read
<3>[ 0.714592] blk_update_request: I/O error, dev mtdblock2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
<3>[ 0.724939] Buffer I/O error on dev mtdblock2, logical block 0, async page read
<1>[ 0.732252] Unable to handle kernel paging request at virtual address ffffffc007fff000
<1>[ 0.740160] Mem abort info:
<1>[ 0.742944] ESR = 0x96000006
<1>[ 0.746001] EC = 0x25: DABT (current EL), IL = 32 bits
<1>[ 0.751303] SET = 0, FnV = 0
<1>[ 0.754347] EA = 0, S1PTW = 0
<1>[ 0.757480] Data abort info:
<1>[ 0.760351] ISV = 0, ISS = 0x00000006
<1>[ 0.764176] CM = 0, WnR = 0
<1>[ 0.767139] swapper pgtable: 4k pages, 39-bit VAs, pgdp=00000000449cd000
<1>[ 0.773828] [ffffffc007fff000] pgd=000000005ffff003, p4d=000000005ffff003, pud=000000005ffff003, pmd=0000000000000000
<0>[ 0.784438] Internal error: Oops: 96000006 [#1] SMP
<7>[ 0.789305] Modules linked in:
<7>[ 0.792355] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G S 5.10.60 #0
<7>[ 0.799740] Hardware name: Linksys E8450 (UBI) (DT)
<7>[ 0.804609] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
<7>[ 0.810612] pc : fdt_check_header+0x4/0x120
<7>[ 0.814788] lr : parse_fit_partitions+0x9c/0x764
<7>[ 0.819395] sp : ffffffc010b8b7d0
<7>[ 0.822699] x29: ffffffc010b8b7d0 x28: 0000000000000000
<7>[ 0.828003] x27: fffffffffffffffb x26: 0000000000000000
<7>[ 0.833307] x25: ffffffc007fff000 x24: 0000000000000000
<7>[ 0.838611] x23: 0000000000000000 x22: ffffffc010b8b8ec
<7>[ 0.843915] x21: 0000000000000000 x20: ffffff8000981200
<7>[ 0.849219] x19: 0000000000000000 x18: 000000000000007c
<7>[ 0.854523] x17: 0000000000000007 x16: 0000000000000007
<7>[ 0.859827] x15: ffffffc010a569e0 x14: 0000000000000174
<7>[ 0.865131] x13: 000000000000007c x12: 0000000000000040
<7>[ 0.870434] x11: 0000000000000000 x10: ffffff80003f2438
<7>[ 0.875739] x9 : 00000000285d2550 x8 : ffffff80009f6140
<7>[ 0.881042] x7 : ffffff8000380820 x6 : 0000000000000001
<7>[ 0.886347] x5 : 00000000000000c0 x4 : 0000000000000002
<7>[ 0.891650] x3 : fffffffeffe20634 x2 : 0000000000000000
<7>[ 0.896954] x1 : ffffffc007fff000 x0 : ffffffc007fff000
<7>[ 0.902258] Call trace:
<7>[ 0.904696] fdt_check_header+0x4/0x120
<7>[ 0.908523] fit_partition+0x20/0x2c
<7>[ 0.912089] blk_add_partitions+0x120/0x510
<7>[ 0.916265] bdev_disk_changed+0xa0/0x12c
<7>[ 0.920265] __blkdev_get+0x4c8/0x650
<7>[ 0.923918] blkdev_get+0x4c/0xd0
<7>[ 0.927225] blkdev_get_by_dev+0x34/0x54
<7>[ 0.931138] __device_add_disk+0x1b0/0x430
<7>[ 0.935225] device_add_disk+0x10/0x1c
<7>[ 0.938968] register_mtd_blktrans_devs+0x6c/0xf0
<7>[ 0.943666] mtd_device_parse_register+0xb8/0x1b0
<7>[ 0.948362] mtk_snand_probe+0x414/0x5a0
<7>[ 0.952279] platform_drv_probe+0x50/0xa0
<7>[ 0.956281] really_probe+0xe4/0x480
<7>[ 0.959847] driver_probe_device+0x54/0xb0
<7>[ 0.963934] device_driver_attach+0xb4/0xc0
<7>[ 0.968108] __driver_attach+0x80/0x114
<7>[ 0.971935] bus_for_each_dev+0x5c/0x90
<7>[ 0.975762] driver_attach+0x20/0x2c
<7>[ 0.979329] bus_add_driver+0xfc/0x1e0
<7>[ 0.983069] driver_register+0x74/0x120
<7>[ 0.986897] __platform_driver_register+0x44/0x50
<7>[ 0.991595] mtk_snand_driver_init+0x18/0x20
<7>[ 0.995857] do_one_initcall+0x4c/0x1b0
<7>[ 0.999687] kernel_init_freeable+0x240/0x2ac
<7>[ 1.004034] kernel_init+0x10/0x10c
<7>[ 1.007514] ret_from_fork+0x10/0x18
<0>[ 1.011084] Code: d2800501 9a813000 d65f03c0 aa0003e1 (b9400000)
<4>[ 1.017171] ---[ end trace d8b54d52f64a2cb3 ]---
root@OpenWrt:~# cat /sys/fs/pstore/dmesg-ramoops-
cat: can't open '/sys/fs/pstore/dmesg-ramoops-': No such file or directory
root@OpenWrt:~# cat /sys/fs/pstore/dmesg-ramoops-1
Panic#2 Part1
<3>[ 0.707136] Buffer I/O error on dev mtdblock2, logical block 0, async page read
<3>[ 0.714592] blk_update_request: I/O error, dev mtdblock2, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
<3>[ 0.724939] Buffer I/O error on dev mtdblock2, logical block 0, async page read
<1>[ 0.732252] Unable to handle kernel paging request at virtual address ffffffc007fff000
<1>[ 0.740160] Mem abort info:
<1>[ 0.742944] ESR = 0x96000006
<1>[ 0.746001] EC = 0x25: DABT (current EL), IL = 32 bits
<1>[ 0.751303] SET = 0, FnV = 0
<1>[ 0.754347] EA = 0, S1PTW = 0
<1>[ 0.757480] Data abort info:
<1>[ 0.760351] ISV = 0, ISS = 0x00000006
<1>[ 0.764176] CM = 0, WnR = 0
<1>[ 0.767139] swapper pgtable: 4k pages, 39-bit VAs, pgdp=00000000449cd000
<1>[ 0.773828] [ffffffc007fff000] pgd=000000005ffff003, p4d=000000005ffff003, pud=000000005ffff003, pmd=0000000000000000
<0>[ 0.784438] Internal error: Oops: 96000006 [#1] SMP
<7>[ 0.789305] Modules linked in:
<7>[ 0.792355] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G S 5.10.60 #0
<7>[ 0.799740] Hardware name: Linksys E8450 (UBI) (DT)
<7>[ 0.804609] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
<7>[ 0.810612] pc : fdt_check_header+0x4/0x120
<7>[ 0.814788] lr : parse_fit_partitions+0x9c/0x764
<7>[ 0.819395] sp : ffffffc010b8b7d0
<7>[ 0.822699] x29: ffffffc010b8b7d0 x28: 0000000000000000
<7>[ 0.828003] x27: fffffffffffffffb x26: 0000000000000000
<7>[ 0.833307] x25: ffffffc007fff000 x24: 0000000000000000
<7>[ 0.838611] x23: 0000000000000000 x22: ffffffc010b8b8ec
<7>[ 0.843915] x21: 0000000000000000 x20: ffffff8000981200
<7>[ 0.849219] x19: 0000000000000000 x18: 000000000000007c
<7>[ 0.854523] x17: 0000000000000007 x16: 0000000000000007
<7>[ 0.859827] x15: ffffffc010a569e0 x14: 0000000000000174
<7>[ 0.865131] x13: 000000000000007c x12: 0000000000000040
<7>[ 0.870434] x11: 0000000000000000 x10: ffffff80003f2438
<7>[ 0.875739] x9 : 00000000285d2550 x8 : ffffff80009f6140
<7>[ 0.881042] x7 : ffffff8000380820 x6 : 0000000000000001
<7>[ 0.886347] x5 : 00000000000000c0 x4 : 0000000000000002
<7>[ 0.891650] x3 : fffffffeffe20634 x2 : 0000000000000000
<7>[ 0.896954] x1 : ffffffc007fff000 x0 : ffffffc007fff000
<7>[ 0.902258] Call trace:
<7>[ 0.904696] fdt_check_header+0x4/0x120
<7>[ 0.908523] fit_partition+0x20/0x2c
<7>[ 0.912089] blk_add_partitions+0x120/0x510
<7>[ 0.916265] bdev_disk_changed+0xa0/0x12c
<7>[ 0.920265] __blkdev_get+0x4c8/0x650
<7>[ 0.923918] blkdev_get+0x4c/0xd0
<7>[ 0.927225] blkdev_get_by_dev+0x34/0x54
<7>[ 0.931138] __device_add_disk+0x1b0/0x430
<7>[ 0.935225] device_add_disk+0x10/0x1c
<7>[ 0.938968] register_mtd_blktrans_devs+0x6c/0xf0
<7>[ 0.943666] mtd_device_parse_register+0xb8/0x1b0
<7>[ 0.948362] mtk_snand_probe+0x414/0x5a0
<7>[ 0.952279] platform_drv_probe+0x50/0xa0
<7>[ 0.956281] really_probe+0xe4/0x480
<7>[ 0.959847] driver_probe_device+0x54/0xb0
<7>[ 0.963934] device_driver_attach+0xb4/0xc0
<7>[ 0.968108] __driver_attach+0x80/0x114
<7>[ 0.971935] bus_for_each_dev+0x5c/0x90
<7>[ 0.975762] driver_attach+0x20/0x2c
<7>[ 0.979329] bus_add_driver+0xfc/0x1e0
<7>[ 0.983069] driver_register+0x74/0x120
<7>[ 0.986897] __platform_driver_register+0x44/0x50
<7>[ 0.991595] mtk_snand_driver_init+0x18/0x20
<7>[ 0.995857] do_one_initcall+0x4c/0x1b0
<7>[ 0.999687] kernel_init_freeable+0x240/0x2ac
<7>[ 1.004034] kernel_init+0x10/0x10c
<7>[ 1.007514] ret_from_fork+0x10/0x18
<0>[ 1.011084] Code: d2800501 9a813000 d65f03c0 aa0003e1 (b9400000)
<4>[ 1.017171] ---[ end trace d8b54d52f64a2cb3 ]---
<0>[ 1.022846] Kernel panic - not syncing: Oops: Fatal exception
<2>[ 1.028584] SMP: stopping secondary CPUs
<0>[ 1.032499] Kernel Offset: disabled
<0>[ 1.035977] CPU features: 0x0000002,04002004
<0>[ 1.040236] Memory Limit: none
I tested twice, and r17421-d98738b5c1 from yesterday works, but r17435-97e32e9702 from today does not. Rather identical errors in pstore on both times.