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Andrew James Wade wrote:
> I've modified stack.c to handle 4k stacks. It can also provide information
> for 8k stacks (fwiw) by changing STACK_GRANULARITY.
>
> It found one stack with only 756 bytes left. I hope it's just due to a
> greedy boot-time function as I'm not running anything particularly exotic.
> (CIFS & Reiser4).
Yes, it does appear to be a boot-time function. It eventually becomes
PID 1, and the stack usage shrinks considerably.
Here is a different approach that uses a kernel module, rather than
/dev/mem. This module will display current stack usage for each PID, as
well as the maximum usage if the kernel has the stack-poison patch.
Also, the current call trace for each PID can be displayed if loaded
with "verbose=1".
for example:
1: init - free stack now: 3640, at max usage: 740
2: ksoftirqd/0 - free stack now: 3880, at max usage: 3788
3: watchdog/0 - free stack now: 3828, at max usage: 3736
4: events/0 - free stack now: 3784, at max usage: 3012
...
Disclaimer: This seems to work for me, but I'm not a very experienced
kernel hacker, so if it breaks, take care that you don't get hurt.
Comments and fixes are welcome.
Thanks,
Frank
- --
Frank Sorenson - KD7TZK
Systems Manager, Computer Science Department
Brigham Young University
[email protected]
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/*
* stack_avail - A linux kernel module to display available stack
* If the kernel stack-poison patch has been applied, this
* module also displays available stack at maximum usage
* Copyright Frank Sorenson <[email protected]> 2005
*
* Permission is hereby granted to copy, modify and redistribute this code
* in terms of the GNU Library General Public License, Version 2 or later,
* at your option.
*
*/
#include <linux/module.h>
#include <linux/kallsyms.h>
static int verbose = 0;
static unsigned long sinittext;
static unsigned long einittext;
static unsigned long stext;
static unsigned long etext;
// task_struct - /UML/Source/Host/linux-2.6.15-rc5-mm3+fs3/include/linux/sched.h
// thread_struct - /UML/Source/Host/linux-2.6.15-rc5-mm3+fs3/include/asm-i386/processor.h
// thread_info - /UML/Source/Host/linux-2.6.15-rc5-mm3+fs3/include/asm-i386/thread_info.h
static inline int valid_stack_ptr(struct thread_info *tinfo, void *p)
{
return p > (void *)tinfo &&
p < (void *)tinfo + THREAD_SIZE - 3;
}
static int core_kernel_text(unsigned long addr)
{
if (addr >= (unsigned long)stext &&
addr <= (unsigned long)etext)
return 1;
if (addr >= (unsigned long)sinittext &&
addr <= (unsigned long)einittext)
return 1;
return 0;
}
int my_kernel_text_address(unsigned long addr)
{
if (core_kernel_text(addr))
return 1;
return 0;
// return __module_text_address(addr) != NULL;
}
static inline unsigned long print_context_stack(struct thread_info *tinfo,
unsigned long *stack, unsigned long ebp)
{
unsigned long addr;
#ifdef CONFIG_FRAME_POINTER
while (valid_stack_ptr(tinfo, (void *)ebp)) {
addr = *(unsigned long *)(ebp + 4);
printk(" [<%08lx>] ", addr);
print_symbol("%s", addr);
printk("\n");
ebp = *(unsigned long *)ebp;
}
#else
while (valid_stack_ptr(tinfo, stack)) {
addr = *stack++;
if (my_kernel_text_address(addr)) {
printk(" [<%08lx>]", addr);
print_symbol(" %s", addr);
printk("\n");
}
}
#endif
return ebp;
}
void show_trace(struct task_struct *task, unsigned long * stack)
{
unsigned long ebp;
ebp = *(unsigned long *) task->thread.esp;
while (1) {
struct thread_info *context;
context = (struct thread_info *)
((unsigned long)stack & (~(THREAD_SIZE - 1)));
ebp = print_context_stack(context, stack, ebp);
stack = (unsigned long*)context->previous_esp;
if (!stack)
break;
printk(" =======================\n");
}
}
static int stack_avail_load(void)
{
struct task_struct *task;
unsigned char *base_addr;
unsigned char *max_addr;
unsigned char *ptr;
unsigned long current_avail;
unsigned long poisoned_avail;
sinittext = kallsyms_lookup_name("_sinittext");
einittext = kallsyms_lookup_name("_einittext");
stext = kallsyms_lookup_name("_stext");
etext = kallsyms_lookup_name("_etext");
printk("Displaying stack space available:\n");
for_each_process(task) {
printk("%d: %s", task->pid, task->comm);
base_addr = (unsigned char *)(task->thread.esp & 0xFFFFF000);
max_addr = base_addr + THREAD_SIZE - 1;
ptr = base_addr + sizeof(struct thread_info);
while (*ptr == 'Q') {
ptr ++;
}
current_avail = (unsigned long)(task->thread.esp) -
(unsigned long)(base_addr) - sizeof(struct thread_info);
poisoned_avail = THREAD_SIZE - ((unsigned long)(max_addr - ptr)) -
sizeof(struct thread_info) - 1;
printk(" - free stack now: %lu", current_avail);
if (poisoned_avail != 0)
printk(", at max usage: %lu", poisoned_avail);
if (verbose) {
printk("\nCurrent call Trace:\n");
show_trace(task, (unsigned long *)(task->thread.esp));
}
printk("\n");
}
return 0;
}
static void stack_avail_unload(void)
{
printk("stack_avail module unloading\n");
}
module_init(stack_avail_load);
module_exit(stack_avail_unload);
module_param(verbose, int, 0);
MODULE_AUTHOR ("Frank Sorenson, [email protected]");
MODULE_DESCRIPTION ("Displays available stack space");
MODULE_LICENSE("GPL");
KVER := $(shell uname -r)
KSRC := /lib/modules/$(KVER)/build
PWD = $(shell pwd)
obj-m += stack_avail.o
all: modules
modules:
$(MAKE) -C $(KSRC) SUBDIRS=$(PWD) BUILD_DIR=$(PWD) modules
ioctl: ioctl.c
$(CC) $< -o $@
clean:
@find . \
\( -name '*.ko' -o -name '.*.cmd' \
-o -name '*.o' -o -name '*.mod.c' \) \
-type f -print | xargs rm -f
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