Re: MIPS r4k cache operations with SMP enabled

[Chris Packham]

On 28/05/19 2:52 PM, Chris Packham wrote:
> Hi,
> 
> I'm trying to port a fairly old Broadcom integrated chip (BCM6818) to
> the latest Linux kernel using the mips/bmips support.
> 
> The chip has a BMIPS4355 core. This has two "thread processors" (cpu
> cores) with separate I-caches but a shared D-cache.
> 
> I've got things booting but I encounter the following BUG()
> 
> BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
> caller is blast_dcache16+0x24/0x154
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.1.0-at1 #5
> Stack : 00000036 8008d0d0 806a0000 807c0000 80754e10 0000000b 80754684
> 8f831c8c
>           80900000 8f828424 807986e7 8071348c 00000000 10008f00 8f831c30
> 7fb69e2a
>           00000000 00000000 80920000 00000056 00002335 00000000 807a0000
> 00000000
>           6d6d3a20 00000000 00000056 73776170 00000000 ffffffff 10008f01
> 807c0000
>           80790000 00002cc2 ffffffff 80900000 00000010 8f83198c 00000000
> 80900000
>           ...
> Call Trace:
> [<8001c208>] show_stack+0x30/0x100
> [<8063282c>] dump_stack+0x9c/0xd0
> [<802f1cec>] debug_smp_processor_id+0xfc/0x110
> [<8002e274>] blast_dcache16+0x24/0x154
> [<80122978>] map_vm_area+0x58/0x70
> [<80123888>] __vmalloc_node_range+0x1fc/0x2b4
> [<80123b54>] vmalloc+0x44/0x50
> [<807d15d0>] jffs2_zlib_init+0x24/0x94
> [<807d1354>] jffs2_compressors_init+0x10/0x30
> [<807d151c>] init_jffs2_fs+0x68/0xf8
> [<8001016c>] do_one_initcall+0x7c/0x1f0
> [<807bee30>] kernel_init_freeable+0x17c/0x258
> [<80650d1c>] kernel_init+0x10/0xf8
> [<80015e6c>] ret_from_kernel_thread+0x14/0x1c
> 
> In blast_dcache16 current_cpu_data is used which invokes
> smp_processor_id() triggering the BUG(). I can fix this by sprinkling
> preempt_disable/preempt_enable through arch/mips/mm/c-r4k.c but that
> seems kind of wrong. Does anyone have any suggestion as to the right way
> to avoid this BUG()?
> 
> Thanks,
> Chris

I think the following might do the trick

---- 8< ----
diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
index 5166e38cd1c6..1fa7f093b59c 100644
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -559,14 +559,19 @@ static inline int has_valid_asid(const struct 
mm_struct *mm, unsigned int type)
         return 0;
  }

-static void r4k__flush_cache_vmap(void)
+static inline void local_r4k_flush_cache(void *args)
  {
         r4k_blast_dcache();
  }

+void r4k__flush_cache_vmap(void)
+{
+       r4k_on_each_cpu(R4K_INDEX, local_r4k_flush_cache, NULL);
+}
+
  static void r4k__flush_cache_vunmap(void)
  {
-       r4k_blast_dcache();
+       r4k_on_each_cpu(R4K_INDEX, local_r4k_flush_cache, NULL);
  }

  /*
@@ -1758,6 +1763,43 @@ static int __init cca_setup(char *str)
         return 0;
  }
---- 8< ----

The rest of the call sites for r4k_blast_dcache() already run with 
preemption disabled.