[PATCH] powerpc/mm/64s: Fix preempt warning in slb_allocate_kernel()

[PATCH] powerpc/mm/64s: Fix preempt warning in slb_allocate_kernel()

[Michael Ellerman]

With preempt enabled we see warnings in do_slb_fault():

  BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u33:0/98
  futex hash table entries: 4096 (order: 3, 524288 bytes)
  caller is do_slb_fault+0x204/0x230
  CPU: 5 PID: 98 Comm: kworker/u33:0 Not tainted 4.19.0-rc3-gcc-7.3.1-00022-g1936f094e164 #138
  Call Trace:
    dump_stack+0xb4/0x104 (unreliable)
    check_preemption_disabled+0x148/0x150
    do_slb_fault+0x204/0x230
    data_access_slb_common+0x138/0x180

This is caused by the get_paca() in slb_allocate_kernel(), which
includes a call to debug_smp_processor_id().

slb_allocate_kernel() can only be called from do_slb_fault(), and in
that path interrupts are hard disabled and so we can't be preempted,
but we can't update the preempt flags (in thread_info) because that
could cause an SLB fault.

So just use local_paca which is safe and doesn't cause the warning.

Fixes: 48e7b7695745 ("powerpc/64s/hash: Convert SLB miss handlers to C")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/mm/slb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
index c3fdf2969d9f..2f5c0a10fac1 100644
--- a/arch/powerpc/mm/slb.c
+++ b/arch/powerpc/mm/slb.c
@@ -715,7 +715,7 @@ static long slb_allocate_kernel(unsigned long ea, unsigned long id)
 			return -EFAULT;
 
 		if (ea < H_VMALLOC_END)
-			flags = get_paca()->vmalloc_sllp;
+			flags = local_paca->vmalloc_sllp;
 		else
 			flags = SLB_VSID_KERNEL | mmu_psize_defs[mmu_io_psize].sllp;
 	} else {
-- 
2.17.2

Re: powerpc/mm/64s: Fix preempt warning in slb_allocate_kernel()

[Michael Ellerman]

On Thu, 2018-11-01 at 05:21:05 UTC, Michael Ellerman wrote:
> With preempt enabled we see warnings in do_slb_fault():
> 
>   BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u33:0/98
>   futex hash table entries: 4096 (order: 3, 524288 bytes)
>   caller is do_slb_fault+0x204/0x230
>   CPU: 5 PID: 98 Comm: kworker/u33:0 Not tainted 4.19.0-rc3-gcc-7.3.1-00022-g1936f094e164 #138
>   Call Trace:
>     dump_stack+0xb4/0x104 (unreliable)
>     check_preemption_disabled+0x148/0x150
>     do_slb_fault+0x204/0x230
>     data_access_slb_common+0x138/0x180
> 
> This is caused by the get_paca() in slb_allocate_kernel(), which
> includes a call to debug_smp_processor_id().
> 
> slb_allocate_kernel() can only be called from do_slb_fault(), and in
> that path interrupts are hard disabled and so we can't be preempted,
> but we can't update the preempt flags (in thread_info) because that
> could cause an SLB fault.
> 
> So just use local_paca which is safe and doesn't cause the warning.
> 
> Fixes: 48e7b7695745 ("powerpc/64s/hash: Convert SLB miss handlers to C")
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Applied to powerpc fixes.

https://git.kernel.org/powerpc/c/c8b00bb742dd036388f37d019dbb9d

cheers