Re: Detailed Stack Information Patch Next Generation

Andrew Morton
2009-06-03T21:07:39Z

> Subject: Detailed Stack Information Patch Next Generation

That's not a very useful patch title. Something like

[patch] procfs: provide stack information for threads

would suit.

On Wed, 03 Jun 2009 22:34:09 +0200
Stefani Seibold <stefani@seibold.net> wrote:

> Hi everybody,
>
> kernel 2.6.30 is near so i think it is time for the next try.
>
> This is the new version of the "detailed stack info" patch which give
> you a better overview of the userland application stack usage,
> especially for embedded linux.
>
> Currently you are only able to dump the main process/thread stack usage
> which is showed in /proc/pid/status by the "VmStk" Value. But you get no
> information about the consumed stack memory of the the threads.
>
> There is an enhancement in the /proc/<pid>/{task/*,}/*maps and which
> marks the vm mapping where the thread stack pointer reside with "[thread
> stack xxxxxxxx]". xxxxxxxx is the start address of the stack.
>
> Also there is a new entry "stack usage" in /proc/<pid>/{task/*,}/status
> which will you give the current stack usage in kb.
>
> I also fixed stack base address in /proc/<pid>/task/*/stat to the base
> address of the associated thread stack and not the one of the main
> process. This makes more sense.
>
> Changes since last posting:
>
> - Redesigned everything what was suggested by Ingo
> - the thread watch monitor is gone
> - the /proc/stackmon entry is also gone
> - slime done
>
> The patch is against 2.6.30-rc7 and tested with on intel and ppc
> architectures.
>
> I think it is now ready for inclusion in the main kernel. Ingo what do
> you think?
>

Missing Signed-off-by:

>
> fs/exec.c | 2 +
> fs/proc/array.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++-
> fs/proc/task_mmu.c | 14 ++++++++++
> include/linux/sched.h | 1
> kernel/fork.c | 3 ++
> 5 files changed, 88 insertions(+), 1 deletion(-)
>
> -patch begins here--------------------------------------------------------------
>
> diff -u -N -r linux-2.6.30.orig/fs/exec.c linux-2.6.30/fs/exec.c
> --- linux-2.6.30.orig/fs/exec.c 2009-06-03 17:36:41.000000000 +0200
> +++ linux-2.6.30/fs/exec.c 2009-06-03 17:30:47.000000000 +0200
> @@ -1328,6 +1328,8 @@
> if (retval < 0)
> goto out;
>
> + current->stack_start = current->mm->start_stack;
> +
> /* execve succeeded */
> current->fs->in_exec = 0;
> current->in_execve = 0;
> diff -u -N -r linux-2.6.30.orig/fs/proc/array.c linux-2.6.30/fs/proc/array.c
> --- linux-2.6.30.orig/fs/proc/array.c 2009-06-03 17:36:41.000000000 +0200
> +++ linux-2.6.30/fs/proc/array.c 2009-06-03 17:32:53.000000000 +0200
> @@ -82,6 +82,7 @@
> #include <linux/pid_namespace.h>
> #include <linux/ptrace.h>
> #include <linux/tracehook.h>
> +#include <linux/pfn.h>
>
> #include <asm/pgtable.h>
> #include <asm/processor.h>
> @@ -321,6 +322,71 @@
> p->nivcsw);
> }
>
> +#ifdef CONFIG_STACK_GROWSUP
> +static inline unsigned long get_stack_pages(struct vm_area_struct *vma,
> + struct task_struct *p)
> +{
> + unsigned long i;
> + struct page *page;
> + unsigned long stack_usage;
> + unsigned long esp;

It's unclear what the units are here. Are they in bytes? Pages? Code
comments and well-chosen identifiers are the way to fix this.

> + esp = KSTK_ESP(p);

So `esp' is in bytes.

> + stack_usage = (PFN_ALIGN(esp)-PFN_ALIGN(p->stack_start));

And `stack_usage' measures bytes

> + for (i = vma->vm_end; i-PAGE_SIZE > esp; i -= PAGE_SIZE) {

And `i' measures bytes

> + page = follow_page(vma, i-PAGE_SIZE, 0);
> +
> + if ((!IS_ERR(page) == 0) || (page))

Why not simply

if (IS_ERR(page) || page)

?

And shouldn't it be !page?

> + break;
> + }
> + return ((i - esp + stack_usage) >> (PAGE_SHIFT)) + 1;

And we return a number-of-pages. Fair enough.

> +}
> +#else
> +static inline unsigned long get_stack_pages(struct vm_area_struct *vma,
> + struct task_struct *p)
> +{
> + unsigned long i;
> + struct page *page;
> + unsigned long stack_usage;
> + unsigned long esp;
> +
> + esp = KSTK_ESP(p);
> +
> + stack_usage = (PFN_ALIGN(p->stack_start) - PFN_ALIGN(esp));
> +
> + for (i = vma->vm_start; i+PAGE_SIZE <= esp; i += PAGE_SIZE) {
> +
> + page = follow_page(vma, i, 0);
> +
> + if ((!IS_ERR(page) == 0) || (page))
> + break;
> + }
> + return ((esp - i + stack_usage) >> (PAGE_SHIFT)) + 1;
> +}

Dittoes.

> +#endif
> +
> +static inline void task_show_stack_usage(struct seq_file *m,
> + struct task_struct *p)
> +{
> + struct vm_area_struct *vma;
> + struct mm_struct *mm;
> +
> + mm = get_task_mm(p);
> +
> + if (mm) {
> + vma = find_vma(mm, p->stack_start);
> +
> + if (vma)
> + seq_printf(m, "Stack usage:\t%lu kB\n",
> + get_stack_pages(vma, p) << (PAGE_SHIFT - 10));

So get_stack_pages() did a bytes-to-pages conversion then its sole
caller does a pages-to-bytes conversion. Can this be simplified?

> +
> + mmput(mm);
> + }
> +}
>
> int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
> struct pid *pid, struct task_struct *task)
> {
> @@ -340,6 +406,7 @@
> task_show_regs(m, task);
> #endif
> task_context_switch_counts(m, task);
> + task_show_stack_usage(m, task);
> return 0;
> }
>
> @@ -481,7 +548,7 @@
> rsslim,
> mm ? mm->start_code : 0,
> mm ? mm->end_code : 0,
> - (permitted && mm) ? mm->start_stack : 0,
> + (permitted) ? task->stack_start : 0,
> esp,
> eip,
> /* The signal information here is obsolete.
> diff -u -N -r linux-2.6.30.orig/fs/proc/task_mmu.c linux-2.6.30/fs/proc/task_mmu.c
> --- linux-2.6.30.orig/fs/proc/task_mmu.c 2009-06-03 17:36:41.000000000 +0200
> +++ linux-2.6.30/fs/proc/task_mmu.c 2009-06-03 17:30:47.000000000 +0200
> @@ -242,6 +242,20 @@
> } else if (vma->vm_start <= mm->start_stack &&
> vma->vm_end >= mm->start_stack) {
> name = "[stack]";
> + } else {
> + unsigned long stack_start;
> +
> + stack_start =
> + ((struct proc_maps_private *)
> + m->private)->task->stack_start;

Like this:

unsiged long stack_start;
struct proc_maps_private *pmp;

pmp = m->private;
stack_start = pmp->task->stack_start;

> + if (vma->vm_start <= stack_start &&
> + vma->vm_end >= stack_start) {
> + pad_len_spaces(m, len);
> + seq_printf(m,
> + "[thread stack: %08lx]",
> + stack_start);
> + }
> }
> } else {
> name = "[vdso]";
> diff -u -N -r linux-2.6.30.orig/include/linux/sched.h linux-2.6.30/include/linux/sched.h
> --- linux-2.6.30.orig/include/linux/sched.h 2009-06-03 17:36:41.000000000 +0200
> +++ linux-2.6.30/include/linux/sched.h 2009-06-03 17:30:47.000000000 +0200
> @@ -1429,6 +1429,7 @@
> /* state flags for use by tracers */
> unsigned long trace;
> #endif
> + unsigned long stack_start;
> };
>
> /* Future-safe accessor for struct task_struct's cpus_allowed. */
> diff -u -N -r linux-2.6.30.orig/kernel/fork.c linux-2.6.30/kernel/fork.c
> --- linux-2.6.30.orig/kernel/fork.c 2009-06-03 17:36:42.000000000 +0200
> +++ linux-2.6.30/kernel/fork.c 2009-06-03 17:30:47.000000000 +0200
> @@ -1092,6 +1092,9 @@
> if (unlikely(current->ptrace))
> ptrace_fork(p, clone_flags);
>
> + p->stack_start = (stack_start == KSTK_ESP(current)) ?
> + current->stack_start : stack_start;
> +

hm. What's this doing?