RISCV: the machanism of available_harts may cause other harts boot failure

[Rick Chen]

Hi,

When I free-run a SMP system, I once hit a failure case where some
harts didn't boot to the kernel shell successfully.
However it can't be duplicated anymore even if I try many times.

But when I set a break during debugging with GDB, it can trigger the
failure case each time.
I think the mechanism of available_harts does not provide a method
that guarantees the success of the SMP system.
Maybe we shall think of a better way for the SMP booting or just remove it ?

Thread 8 hit Breakpoint 1, harts_early_init ()

(gdb) c
Continuing.
[Switching to Thread 7]

Thread 7 hit Breakpoint 1, harts_early_init ()

(gdb)
Continuing.
[Switching to Thread 6]

Thread 6 hit Breakpoint 1, harts_early_init ()

(gdb)
Continuing.
[Switching to Thread 5]

Thread 5 hit Breakpoint 1, harts_early_init ()

(gdb)
Continuing.
[Switching to Thread 4]

Thread 4 hit Breakpoint 1, harts_early_init ()

(gdb)
Continuing.
[Switching to Thread 3]

Thread 3 hit Breakpoint 1, harts_early_init ()
(gdb)
Continuing.
[Switching to Thread 2]

Thread 2 hit Breakpoint 1, harts_early_init ()
(gdb)
Continuing.
[Switching to Thread 1]

Thread 1 hit Breakpoint 1, harts_early_init ()
(gdb)
Continuing.
[Switching to Thread 5]


Thread 5 hit Breakpoint 3, 0x0000000001200000 in ?? ()
(gdb) info threads
  Id   Target Id         Frame
  1    Thread 1 (hart 1) secondary_hart_loop () at arch/riscv/cpu/start.S:436
  2    Thread 2 (hart 2) secondary_hart_loop () at arch/riscv/cpu/start.S:436
  3    Thread 3 (hart 3) secondary_hart_loop () at arch/riscv/cpu/start.S:436
  4    Thread 4 (hart 4) secondary_hart_loop () at arch/riscv/cpu/start.S:436
* 5    Thread 5 (hart 5) 0x0000000001200000 in ?? ()
  6    Thread 6 (hart 6) 0x000000000000b650 in ?? ()
  7    Thread 7 (hart 7) 0x000000000000b650 in ?? ()
  8    Thread 8 (hart 8) 0x0000000000005fa0 in ?? ()
(gdb) c
Continuing.



[    0.175619] smp: Bringing up secondary CPUs ...
[    1.230474] CPU1: failed to come online
[    2.282349] CPU2: failed to come online
[    3.334394] CPU3: failed to come online
[    4.386783] CPU4: failed to come online
[    4.427829] smp: Brought up 1 node, 4 CPUs


/root # cat /proc/cpuinfo
processor       : 0
hart            : 4
isa     : rv64i2p0m2p0a2p0c2p0xv5-1p1
mmu             : sv39

processor       : 5
hart            : 5
isa     : rv64i2p0m2p0a2p0c2p0xv5-1p1
mmu             : sv39

processor       : 6
hart            : 6
isa     : rv64i2p0m2p0a2p0c2p0xv5-1p1
mmu             : sv39

processor       : 7
hart            : 7
isa     : rv64i2p0m2p0a2p0c2p0xv5-1p1
mmu             : sv39

/root #

Thanks,
Rick