[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>

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);
 }

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;
 }

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.

include/asm-i386/current.h

@@ -1,13 +1,14 @@
 #ifndef _I386_CURRENT_H
 #define _I386_CURRENT_H
 
-#include <linux/thread_info.h>
+#include <asm/pda.h>
+#include <linux/compiler.h>
 
 struct task_struct;
 
-static __always_inline struct task_struct * get_current(void)
+static __always_inline struct task_struct *get_current(void)
 {
-	return current_thread_info()->task;
+	return read_pda(pcurrent);
 }
 
 #define current get_current()

include/asm-i386/pda.h

@@ -7,12 +7,14 @@
 #define _I386_PDA_H
 
 #include <linux/stddef.h>
+#include <linux/types.h>
 
 struct i386_pda
 {
 	struct i386_pda *_pda;		/* pointer to self */
 
 	int cpu_number;
+	struct task_struct *pcurrent;	/* current process */
 };
 
 extern struct i386_pda *_cpu_pda[];