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Subject[PATCH 2/4 v2] x86: Remove previous_esp from i386 thread_info structure
From: Steven Rostedt <srostedt@redhat.com>

The i386 thread_info contains a previous_esp field that is used
to daisy chain the different stacks for dump_stack()
(ie. irq, softirq, thread stacks).

The goal is to eventual make i386 handling of thread_info the same
as x86_64, which means that the thread_info will not be in the stack
but as a per_cpu variable. We will no longer depend on thread_info
being able to daisy chain different stacks as it will only exist
in one location (the thread stack).

By moving previous_esp out of thread_info, and just placing it
above the thread_info of the current stack, we can still use
the stacks to daisy chain which stack was in use when preempted by
an interrupt.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/include/asm/thread_info.h | 5 -----
arch/x86/kernel/dumpstack_32.c | 10 +++++++++-
arch/x86/kernel/irq_32.c | 13 +++++++++----
3 files changed, 18 insertions(+), 10 deletions(-)
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 625910f..8f2b249 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -34,11 +34,6 @@ struct thread_info {
mm_segment_t addr_limit;
struct restart_block restart_block;
void __user *sysenter_return;
-#ifdef CONFIG_X86_32
- unsigned long previous_esp; /* ESP of the previous stack in
- case of nested (IRQ) stacks
- */
-#endif
int uaccess_err;
};

diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index 3b97a80..8955e25 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -22,6 +22,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
const struct stacktrace_ops *ops, void *data)
{
int graph = 0;
+ u32 *prev_esp;

if (!task)
task = current;
@@ -44,9 +45,16 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
((unsigned long)stack & (~(THREAD_SIZE - 1)));
bp = ops->walk_stack(context, stack, bp, ops, data, NULL, &graph);

- stack = (unsigned long *)context->previous_esp;
+ /* Stop if not on irq stack */
+ if (task_stack_page(task) == context)
+ break;
+
+ /* The previous esp is just above the context */
+ prev_esp = (u32 *) ((char *)context + sizeof(struct thread_info));
+ stack = (unsigned long *)*prev_esp;
if (!stack)
break;
+
if (ops->stack(data, "IRQ") < 0)
break;
touch_nmi_watchdog();
diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 7209070..47909a0 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -76,7 +76,7 @@ static inline int
execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq)
{
union irq_ctx *curctx, *irqctx;
- u32 *isp, arg1, arg2;
+ u32 *isp, *prev_esp, arg1, arg2;

curctx = (union irq_ctx *) current_thread_info();
irqctx = __this_cpu_read(hardirq_ctx);
@@ -93,7 +93,9 @@ execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq)
/* build the stack frame on the IRQ stack */
isp = (u32 *) ((char *)irqctx + sizeof(*irqctx));
irqctx->tinfo.task = curctx->tinfo.task;
- irqctx->tinfo.previous_esp = current_stack_pointer;
+ /* Save the next esp after thread_info */
+ prev_esp = (u32 *) ((char *)irqctx + sizeof(struct thread_info));
+ *prev_esp = current_stack_pointer;

/*
* Copy the softirq bits in preempt_count so that the
@@ -154,7 +156,7 @@ asmlinkage void do_softirq(void)
unsigned long flags;
struct thread_info *curctx;
union irq_ctx *irqctx;
- u32 *isp;
+ u32 *isp, *prev_esp;

if (in_interrupt())
return;
@@ -165,11 +167,14 @@ asmlinkage void do_softirq(void)
curctx = current_thread_info();
irqctx = __this_cpu_read(softirq_ctx);
irqctx->tinfo.task = curctx->task;
- irqctx->tinfo.previous_esp = current_stack_pointer;

/* build the stack frame on the softirq stack */
isp = (u32 *) ((char *)irqctx + sizeof(*irqctx));

+ /* Push the previous esp onto the stack */
+ prev_esp = (u32 *) ((char *)irqctx + sizeof(struct thread_info));
+ *prev_esp = current_stack_pointer;
+
call_on_stack(__do_softirq, isp);
/*
* Shouldn't happen, we returned above if in_interrupt():
--
1.7.5.4



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