MIPS: Fix accessing to per-cpu data when flushing the cache

This fixes the following issue

BUG: using smp_processor_id() in preemptible [00000000] code: kjournald/1761
caller is blast_dcache32+0x30/0x254
Call Trace:
[<8047f02c>] dump_stack+0x8/0x34
[<802e7e40>] debug_smp_processor_id+0xe0/0xf0
[<80114d94>] blast_dcache32+0x30/0x254
[<80118484>] r4k_dma_cache_wback_inv+0x200/0x288
[<80110ff0>] mips_dma_map_sg+0x108/0x180
[<80355098>] ide_dma_prepare+0xf0/0x1b8
[<8034eaa4>] do_rw_taskfile+0x1e8/0x33c
[<8035951c>] ide_do_rw_disk+0x298/0x3e4
[<8034a3c4>] do_ide_request+0x2e0/0x704
[<802bb0dc>] __blk_run_queue+0x44/0x64
[<802be000>] queue_unplugged.isra.36+0x1c/0x54
[<802beb94>] blk_flush_plug_list+0x18c/0x24c
[<802bec6c>] blk_finish_plug+0x18/0x48
[<8026554c>] journal_commit_transaction+0x3b8/0x151c
[<80269648>] kjournald+0xec/0x238
[<8014ac00>] kthread+0xb8/0xc0
[<8010268c>] ret_from_kernel_thread+0x14/0x1c

Caches in most systems are identical - but not always, so we can't avoid
the use of smp_call_function() by just looking at the boot CPU's data,
have to fiddle with preemption instead.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5835

arch/mips/mm/c-r4k.c

@@ -12,6 +12,7 @@
 #include <linux/highmem.h>
 #include <linux/kernel.h>
 #include <linux/linkage.h>
+#include <linux/preempt.h>
 #include <linux/sched.h>
 #include <linux/smp.h>
 #include <linux/mm.h>
@@ -601,6 +602,7 @@ static void r4k_dma_cache_wback_inv(unsigned long addr, unsigned long size)
 	/* Catch bad driver code */
 	BUG_ON(size == 0);
 
+	preempt_disable();
 	if (cpu_has_inclusive_pcaches) {
 		if (size >= scache_size)
 			r4k_blast_scache();
@@ -621,6 +623,7 @@ static void r4k_dma_cache_wback_inv(unsigned long addr, unsigned long size)
 		R4600_HIT_CACHEOP_WAR_IMPL;
 		blast_dcache_range(addr, addr + size);
 	}
+	preempt_enable();
 
 	bc_wback_inv(addr, size);
 	__sync();
@@ -631,6 +634,7 @@ static void r4k_dma_cache_inv(unsigned long addr, unsigned long size)
 	/* Catch bad driver code */
 	BUG_ON(size == 0);
 
+	preempt_disable();
 	if (cpu_has_inclusive_pcaches) {
 		if (size >= scache_size)
 			r4k_blast_scache();
@@ -655,6 +659,7 @@ static void r4k_dma_cache_inv(unsigned long addr, unsigned long size)
 		R4600_HIT_CACHEOP_WAR_IMPL;
 		blast_inv_dcache_range(addr, addr + size);
 	}
+	preempt_enable();
 
 	bc_inv(addr, size);
 	__sync();