Re: [Crash-utility] [PATCH] Fix x86 initialization for {hard, soft}irq_ctx
----- Original Message -----
Current code is setting {hard,soft}irq_ctx[] to (irq_ctx **), because
per_cpu symbol itself is pointer of specified type (irq_ctx *).
But, I wonder how this works in past, the code is expecting
{hard,soft}_ctx[] are (irq_ctx *). This fixes by deref per_cpu in
initialization, and set expected pointers.
Tested on i386 v3.10.
You are correct -- apparently it never did work.
The reason why I never noticed with RHEL kernels is that up until linux-2.6.29,
the IRQ stacks were declared as a static NR_CPUS-bounded array:
#ifdef CONFIG_4KSTACKS
/*
* per-CPU IRQ handling contexts (thread information and stack)
*/
union irq_ctx {
struct thread_info tinfo;
u32 stack[THREAD_SIZE/sizeof(u32)];
};
static union irq_ctx *hardirq_ctx[NR_CPUS] __read_mostly;
static union irq_ctx *softirq_ctx[NR_CPUS] __read_mostly;
static char softirq_stack[NR_CPUS * THREAD_SIZE] __page_aligned_bss;
static char hardirq_stack[NR_CPUS * THREAD_SIZE] __page_aligned_bss;
Then in linux-2.6.30, they were changed to be per-cpu variables:
#ifdef CONFIG_4KSTACKS
/*
* per-CPU IRQ handling contexts (thread information and stack)
*/
union irq_ctx {
struct thread_info tinfo;
u32 stack[THREAD_SIZE/sizeof(u32)];
} __attribute__((aligned(PAGE_SIZE)));
static DEFINE_PER_CPU(union irq_ctx *, hardirq_ctx);
static DEFINE_PER_CPU(union irq_ctx *, softirq_ctx);
static DEFINE_PER_CPU_PAGE_ALIGNED(union irq_ctx, hardirq_stack);
static DEFINE_PER_CPU_PAGE_ALIGNED(union irq_ctx, softirq_stack);
We never ran into the bug in 32-bit x86 RHEL6 (2.6.32-based) kernels because
we did not configure CONFIG_4KSTACKS.
Later on, the CONFIG_4KSTACKS restriction looks like it was removed, but we
stopped supporting 32-bit x86 in RHEL7. And nobody ever reported it from any
other x86 kernel sources.
I also note that in linux-3.15 the data structure name and variables were
changed to:
struct irq_stack {
u32 stack[THREAD_SIZE/sizeof(u32)];
} __aligned(THREAD_SIZE);
DECLARE_PER_CPU(struct irq_stack *, hardirq_stack);
DECLARE_PER_CPU(struct irq_stack *, softirq_stack);
So your patch would need more work for 3.15 and later kernels.
Thanks,
Dave
---
task.c | 28 ++++++++++++++++++++++++----
1 file changed, 24 insertions(+), 4 deletions(-)
diff -puN task.c~ia32-irq-stack-fix task.c
--- crash-64/task.c~ia32-irq-stack-fix 2017-02-08 17:37:33.126367767 +0900
+++ crash-64-hirofumi/task.c 2017-02-08 17:46:06.900703326 +0900
@@ -570,10 +570,20 @@ irqstacks_init(void)
if ((hard_sp = per_cpu_symbol_search("per_cpu__hardirq_ctx"))) {
if ((kt->flags & SMP) && (kt->flags & PER_CPU_OFF)) {
for (i = 0; i < NR_CPUS; i++) {
+ ulong ptr;
+
if (!kt->__per_cpu_offset[i])
continue;
- tt->hardirq_ctx[i] = hard_sp->value +
- kt->__per_cpu_offset[i];
+ ptr = hard_sp->value + kt->__per_cpu_offset[i];
+
+ if (!readmem(ptr, KVADDR, &ptr,
+ sizeof(void *), "hardirq ctx",
+ RETURN_ON_ERROR)) {
+ error(INFO, "cannot read hardirq_ctx[%d] at %lx\n",
+ i, ptr);
+ continue;
+ }
+ tt->hardirq_ctx[i] = ptr;
}
} else
tt->hardirq_ctx[0] = hard_sp->value;
@@ -604,10 +614,20 @@ irqstacks_init(void)
if ((soft_sp = per_cpu_symbol_search("per_cpu__softirq_ctx"))) {
if ((kt->flags & SMP) && (kt->flags & PER_CPU_OFF)) {
for (i = 0; i < NR_CPUS; i++) {
+ ulong ptr;
+
if (!kt->__per_cpu_offset[i])
continue;
- tt->softirq_ctx[i] = soft_sp->value +
- kt->__per_cpu_offset[i];
+ ptr = soft_sp->value + kt->__per_cpu_offset[i];
+
+ if (!readmem(ptr, KVADDR, &ptr,
+ sizeof(void *), "softirq ctx",
+ RETURN_ON_ERROR)) {
+ error(INFO, "cannot read softirq_ctx[%d] at %lx\n",
+ i, ptr);
+ continue;
+ }
+ tt->softirq_ctx[i] = ptr;
}
} else
tt->softirq_ctx[0] = soft_sp->value;
--
OGAWA Hirofumi <hirofumi mail parknet co jp>