[PATCH] i386: Implement "current" with the PDA

Use the pcurrent field in the PDA to implement the "current" macro.  This ends
up compiling down to a single instruction to get the current task.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Chuck Ebbert <76306.1226@compuserve.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>

3 files changed, 5 insertions, 0 deletions

diff --git a/arch/i386/kernel/asm-offsets.c b/arch/i386/kernel/asm-offsets.c
index 85f1b038e9c3..0666eb0ed7bc 100644
--- a/arch/i386/kernel/asm-offsets.c
+++ b/arch/i386/kernel/asm-offsets.c
@@ -15,6 +15,7 @@
 #include <asm/processor.h>
 #include <asm/thread_info.h>
 #include <asm/elf.h>
+#include <asm/pda.h>
 
 #define DEFINE(sym, val) \
         asm volatile("\n->" #sym " %0 " #val : : "i" (val))
@@ -99,4 +100,5 @@ void foo(void)
 
         BLANK();
         OFFSET(PDA_cpu, i386_pda, cpu_number);
+        OFFSET(PDA_pcurrent, i386_pda, pcurrent);
 }
diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c
index e476202b887f..6958ae5e2fa5 100644
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -651,6 +651,7 @@ __cpuinit int alloc_gdt(int cpu)
 struct i386_pda boot_pda = {
         ._pda = &boot_pda,
         .cpu_number = 0,
+        .pcurrent = &init_task,
 };
 
 static inline void set_kernel_gs(void)
@@ -696,6 +697,7 @@ __cpuinit int init_gdt(int cpu, struct task_struct *idle)
         memset(pda, 0, sizeof(*pda));
         pda->_pda = pda;
         pda->cpu_number = cpu;
+        pda->pcurrent = idle;
 
         return 1;
 }
diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index dc4272545179..8749b10d3805 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -684,6 +684,7 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
         if (unlikely(prev->fs | next->fs))
                 loadsegment(fs, next->fs);
 
+        write_pda(pcurrent, next_p);
 
         /*
          * Restore IOPL if needed.