Re: [RFC][PATCH] x86 transition to 4k stacks (3/3)

[Dave Hansen <haveblue@us.ibm.com>]

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Dipankar Sarma wrote:
> On Tue, Oct 15, 2002 at 08:10:08AM +0200, Dave Hansen wrote:
> 
>>* interrupt stacks (3/3)
>>    - allocate per-cpu interrupt stacks.  upon entry to
>>      common_interrupt, switch to the current cpu's stack.
>>    - inherit the interrupted task's preempt count
> 
> Adding current->thread_info->preempt_count doesn't make sense. What
> you need to do is to copy the old thread_info->preempt_count to
> new thread_info->preempt_count. If you aren't switching stack
> this has no effect.

Right you are.

> 	movl TI_PRE_COUNT(%ebx),%ecx
> 	movl %ecx,TI_PRE_COUNT(%esi)
> 
> So if you are not switching stack, %ebx == %esi and this has no effect.
> The preempt_count() manipulation in do_IRQ() should be deleted.
> 
> And, no you can't weasel out of x86 assembly  :)

Updated patch is attached.

-- 
Dave Hansen
haveblue@us.ibm.com

[-- Attachment #2: interrupt_stacks-2.5.42+bk-7.patch --]
[-- Type: text/plain, Size: 9093 bytes --]

# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
#	           ChangeSet	1.852   -> 1.856  
#	arch/i386/kernel/process.c	1.33    -> 1.34   
#	arch/i386/kernel/irq.c	1.21    -> 1.25   
#	include/asm-i386/thread_info.h	1.8     -> 1.9    
#	arch/i386/kernel/entry.S	1.39    -> 1.41   
#	 arch/i386/config.in	1.57    -> 1.58   
#	arch/i386/kernel/smpboot.c	1.35    -> 1.36   
#	arch/i386/kernel/init_task.c	1.7     -> 1.8    
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 02/10/14	haveblue@elm3b96.(none)	1.851.1.1
# interrupt_stacks-tmp.patch
# --------------------------------------------
#
diff -Nru a/arch/i386/config.in b/arch/i386/config.in
--- a/arch/i386/config.in	Tue Oct 15 11:13:17 2002
+++ b/arch/i386/config.in	Tue Oct 15 11:13:17 2002
@@ -34,6 +34,7 @@
 #
 # Define implied options from the CPU selection here
 #
+define_bool CONFIG_X86_HAVE_CMOV n
 
 if [ "$CONFIG_M386" = "y" ]; then
    define_bool CONFIG_X86_CMPXCHG n
@@ -90,18 +91,21 @@
    define_bool CONFIG_X86_GOOD_APIC y
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
    define_bool CONFIG_X86_PPRO_FENCE y
+   define_bool CONFIG_X86_HAVE_CMOV y
 fi
 if [ "$CONFIG_MPENTIUMIII" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5
    define_bool CONFIG_X86_TSC y
    define_bool CONFIG_X86_GOOD_APIC y
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
+   define_bool CONFIG_X86_HAVE_CMOV y
 fi
 if [ "$CONFIG_MPENTIUM4" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 7
    define_bool CONFIG_X86_TSC y
    define_bool CONFIG_X86_GOOD_APIC y
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
+   define_bool CONFIG_X86_HAVE_CMOV y
 fi
 if [ "$CONFIG_MK6" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5
@@ -115,6 +119,7 @@
    define_bool CONFIG_X86_GOOD_APIC y
    define_bool CONFIG_X86_USE_3DNOW y
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
+   define_bool CONFIG_X86_HAVE_CMOV y
 fi
 if [ "$CONFIG_MELAN" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 4
@@ -131,6 +136,7 @@
 if [ "$CONFIG_MCRUSOE" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5
    define_bool CONFIG_X86_TSC y
+   define_bool CONFIG_X86_HAVE_CMOV y
 fi
 if [ "$CONFIG_MWINCHIPC6" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5
diff -Nru a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
--- a/arch/i386/kernel/entry.S	Tue Oct 15 11:13:17 2002
+++ b/arch/i386/kernel/entry.S	Tue Oct 15 11:13:17 2002
@@ -334,7 +334,45 @@
 	ALIGN
 common_interrupt:
 	SAVE_ALL
+
+
+	GET_THREAD_INFO(%ebx)
+	movl TI_IRQ_STACK(%ebx),%ecx
+	movl TI_TASK(%ebx),%edx
+	movl %esp,%eax
+	leal (THREAD_SIZE-4)(%ecx),%esi # %ecx+THREAD_SIZE is next stack
+	                                # -4 keeps us in the right one
+	testl %ecx,%ecx                 # is there a valid irq_stack?
+
+	# switch to the irq stack
+#ifdef CONFIG_X86_HAVE_CMOV
+	cmovnz %esi,%esp
+#else
+	jz 1f
+	mov %esi,%esp
+1:
+#endif
+	
+	# update the task pointer in the irq stack
+	GET_THREAD_INFO(%esi)
+	movl %edx,TI_TASK(%esi)
+
+	# update the preempt count in the irq stack
+	movl TI_PRE_COUNT(%ebx),%ecx
+	movl %ecx,TI_PRE_COUNT(%esi)
+		
 	call do_IRQ
+
+	movl %eax,%esp                  # potentially restore non-irq stack
+	
+	# copy flags from the irq stack back into the task's thread_info
+	# %esi is saved over the do_IRQ call and contains the irq stack
+	# thread_info pointer
+	# %ebx contains the original thread_info pointer
+	movl TI_FLAGS(%esi),%eax
+	movl $0,TI_FLAGS(%esi)
+	LOCK orl %eax,TI_FLAGS(%ebx)
+
 	jmp ret_from_intr
 
 #define BUILD_INTERRUPT(name, nr)	\
diff -Nru a/arch/i386/kernel/init_task.c b/arch/i386/kernel/init_task.c
--- a/arch/i386/kernel/init_task.c	Tue Oct 15 11:13:17 2002
+++ b/arch/i386/kernel/init_task.c	Tue Oct 15 11:13:17 2002
@@ -13,6 +13,9 @@
 static struct signal_struct init_signals = INIT_SIGNALS(init_signals);
 struct mm_struct init_mm = INIT_MM(init_mm);
 
+union thread_union init_irq_union
+	__attribute__((__section__(".data.init_task")));
+
 #ifdef CONFIG_X86_STACK_CHECK
 union thread_union stack_overflow_stack
 	__attribute__((__section__(".data.init_task")));
diff -Nru a/arch/i386/kernel/irq.c b/arch/i386/kernel/irq.c
--- a/arch/i386/kernel/irq.c	Tue Oct 15 11:13:17 2002
+++ b/arch/i386/kernel/irq.c	Tue Oct 15 11:13:17 2002
@@ -311,7 +311,8 @@
  * SMP cross-CPU interrupts have their own specific
  * handlers).
  */
-asmlinkage unsigned int do_IRQ(struct pt_regs regs)
+struct pt_regs *do_IRQ(struct pt_regs *regs) __attribute__((regparm(1)));
+struct pt_regs *do_IRQ(struct pt_regs *regs)
 {	
 	/* 
 	 * We ack quickly, we don't want the irq controller
@@ -323,7 +324,7 @@
 	 * 0 return value means that this irq is already being
 	 * handled by some other CPU. (or is disabled)
 	 */
-	int irq = regs.orig_eax & 0xff; /* high bits used in ret_from_ code  */
+	int irq = regs->orig_eax & 0xff; /* high bits used in ret_from_ code  */
 	int cpu = smp_processor_id();
 	irq_desc_t *desc = irq_desc + irq;
 	struct irqaction * action;
@@ -373,7 +374,7 @@
 	 */
 	for (;;) {
 		spin_unlock(&desc->lock);
-		handle_IRQ_event(irq, &regs, action);
+		handle_IRQ_event(irq, regs, action);
 		spin_lock(&desc->lock);
 		
 		if (likely(!(desc->status & IRQ_PENDING)))
@@ -392,7 +393,7 @@
 
 	irq_exit();
 
-	return 1;
+	return regs;
 }
 
 /**
diff -Nru a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
--- a/arch/i386/kernel/process.c	Tue Oct 15 11:13:17 2002
+++ b/arch/i386/kernel/process.c	Tue Oct 15 11:13:17 2002
@@ -427,6 +427,7 @@
 
 	/* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
 
+	next_p->thread_info->irq_stack = prev_p->thread_info->irq_stack;
 	unlazy_fpu(prev_p);
 
 	/*
diff -Nru a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
--- a/arch/i386/kernel/smpboot.c	Tue Oct 15 11:13:17 2002
+++ b/arch/i386/kernel/smpboot.c	Tue Oct 15 11:13:17 2002
@@ -69,6 +69,11 @@
 /* Per CPU bogomips and other parameters */
 struct cpuinfo_x86 cpu_data[NR_CPUS] __cacheline_aligned;
 
+/* Per CPU interrupt stacks */
+extern union thread_union init_irq_union;
+union thread_union *irq_stacks[NR_CPUS] __cacheline_aligned =
+	{ &init_irq_union, };
+
 /* Set when the idlers are all forked */
 int smp_threads_ready;
 
@@ -763,6 +768,28 @@
 	return (send_status | accept_status);
 }
 
+static void __init setup_irq_stack(struct task_struct *p, int cpu)
+{
+	unsigned long stk;
+
+	stk = __get_free_pages(GFP_KERNEL, THREAD_ORDER+1);
+	if (!stk)
+		panic("I can't seem to allocate my irq stack.  Oh well, giving up.");
+
+	irq_stacks[cpu] = (void *)stk;
+	memset(irq_stacks[cpu], 0, THREAD_SIZE);
+	irq_stacks[cpu]->thread_info.cpu = cpu;
+	irq_stacks[cpu]->thread_info.preempt_count = 1;
+					/* interrupts are not preemptable */
+	p->thread_info->irq_stack = irq_stacks[cpu];
+
+	/* If we want to make the irq stack more than one unit
+	 * deep, we can chain then off of the irq_stack pointer
+	 * here.
+	 */
+}
+
+
 extern unsigned long cpu_initialized;
 
 static void __init do_boot_cpu (int apicid) 
@@ -786,6 +813,8 @@
 	if (IS_ERR(idle))
 		panic("failed fork for CPU %d", cpu);
 
+	setup_irq_stack(idle, cpu);
+
 	/*
 	 * We remove it from the pidhash and the runqueue
 	 * once we got the process:
@@ -803,7 +832,13 @@
 
 	/* So we see what's up   */
 	printk("Booting processor %d/%d eip %lx\n", cpu, apicid, start_eip);
-	stack_start.esp = (void *) (1024 + PAGE_SIZE + (char *)idle->thread_info);
+
+	/* The -4 is to correct for the fact that the stack pointer
+	 * is used to find the location of the thread_info structure
+	 * by masking off several of the LSBs.  Without the -4, esp
+	 * is pointing to the page after the one the stack is on.
+	 */
+	stack_start.esp = (void *)(THREAD_SIZE - 4 + (char *)idle->thread_info);
 
 	/*
 	 * This grunge runs the startup process for
diff -Nru a/include/asm-i386/thread_info.h b/include/asm-i386/thread_info.h
--- a/include/asm-i386/thread_info.h	Tue Oct 15 11:13:17 2002
+++ b/include/asm-i386/thread_info.h	Tue Oct 15 11:13:17 2002
@@ -29,9 +29,11 @@
 	__s32			preempt_count; /* 0 => preemptable, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
+						   0 for interrupts: illegal
 					 	   0-0xBFFFFFFF for user-thead
 						   0-0xFFFFFFFF for kernel-thread
 						*/
+	struct thread_info	*irq_stack;	/* pointer to cpu irq stack */
 
 	__u8			supervisor_stack[0];
 };
@@ -45,6 +47,7 @@
 #define TI_CPU		0x0000000C
 #define TI_PRE_COUNT	0x00000010
 #define TI_ADDR_LIMIT	0x00000014
+#define TI_IRQ_STACK	0x00000018
 
 #endif
 
@@ -59,6 +62,7 @@
 #define INIT_THREAD_SIZE       THREAD_SIZE
 
 #ifndef __ASSEMBLY__
+
 #define INIT_THREAD_INFO(tsk)			\
 {						\
 	.task		= &tsk,         	\
@@ -67,8 +71,9 @@
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
 	.addr_limit	= KERNEL_DS,		\
+	.irq_stack	= &init_irq_union	\
 }
-
+			
 #define init_thread_info	(init_thread_union.thread_info)
 #define init_stack		(init_thread_union.stack)