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Subject[07/39] revert "procfs: provide stack information for threads" and its fixup commits

2.6.33-stable review patch. If anyone has any objections, please let us know.

------------------
From: Robin Holt <holt@sgi.com>

commit 34441427aab4bdb3069a4ffcda69a99357abcb2e upstream.

Originally, commit d899bf7b ("procfs: provide stack information for
threads") attempted to introduce a new feature for showing where the
threadstack was located and how many pages are being utilized by the
stack.

Commit c44972f1 ("procfs: disable per-task stack usage on NOMMU") was
applied to fix the NO_MMU case.

Commit 89240ba0 ("x86, fs: Fix x86 procfs stack information for threads on
64-bit") was applied to fix a bug in ia32 executables being loaded.

Commit 9ebd4eba7 ("procfs: fix /proc/<pid>/stat stack pointer for kernel
threads") was applied to fix a bug which had kernel threads printing a
userland stack address.

Commit 1306d603f ('proc: partially revert "procfs: provide stack
information for threads"') was then applied to revert the stack pages
being used to solve a significant performance regression.

This patch nearly undoes the effect of all these patches.

The reason for reverting these is it provides an unusable value in
field 28. For x86_64, a fork will result in the task->stack_start
value being updated to the current user top of stack and not the stack
start address. This unpredictability of the stack_start value makes
it worthless. That includes the intended use of showing how much stack
space a thread has.

Other architectures will get different values. As an example, ia64
gets 0. The do_fork() and copy_process() functions appear to treat the
stack_start and stack_size parameters as architecture specific.

I only partially reverted c44972f1 ("procfs: disable per-task stack usage
on NOMMU") . If I had completely reverted it, I would have had to change
mm/Makefile only build pagewalk.o when CONFIG_PROC_PAGE_MONITOR is
configured. Since I could not test the builds without significant effort,
I decided to not change mm/Makefile.

I only partially reverted 89240ba0 ("x86, fs: Fix x86 procfs stack
information for threads on 64-bit") . I left the KSTK_ESP() change in
place as that seemed worthwhile.

Signed-off-by: Robin Holt <holt@sgi.com>
Cc: Stefani Seibold <stefani@seibold.net>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
Documentation/filesystems/proc.txt | 3 +--
fs/compat.c | 2 --
fs/exec.c | 2 --
fs/proc/array.c | 3 +--
fs/proc/task_mmu.c | 19 -------------------
include/linux/sched.h | 1 -
kernel/fork.c | 2 --
7 files changed, 2 insertions(+), 30 deletions(-)

--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -308,7 +308,7 @@ address perms offset dev in
08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
a7cb1000-a7cb2000 ---p 00000000 00:00 0
-a7cb2000-a7eb2000 rw-p 00000000 00:00 0 [threadstack:001ff4b4]
+a7cb2000-a7eb2000 rw-p 00000000 00:00 0
a7eb2000-a7eb3000 ---p 00000000 00:00 0
a7eb3000-a7ed5000 rw-p 00000000 00:00 0
a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
@@ -344,7 +344,6 @@ is not associated with a file:
[stack] = the stack of the main process
[vdso] = the "virtual dynamic shared object",
the kernel system call handler
- [threadstack:xxxxxxxx] = the stack of the thread, xxxxxxxx is the stack size

or if empty, the mapping is anonymous.

--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1530,8 +1530,6 @@ int compat_do_execve(char * filename,
if (retval < 0)
goto out;

- current->stack_start = current->mm->start_stack;
-
/* execve succeeded */
current->fs->in_exec = 0;
current->in_execve = 0;
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1386,8 +1386,6 @@ int do_execve(char * filename,
if (retval < 0)
goto out;

- current->stack_start = current->mm->start_stack;
-
/* execve succeeded */
current->fs->in_exec = 0;
current->in_execve = 0;
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -82,7 +82,6 @@
#include <linux/pid_namespace.h>
#include <linux/ptrace.h>
#include <linux/tracehook.h>
-#include <linux/swapops.h>

#include <asm/pgtable.h>
#include <asm/processor.h>
@@ -494,7 +493,7 @@ static int do_task_stat(struct seq_file
rsslim,
mm ? mm->start_code : 0,
mm ? mm->end_code : 0,
- (permitted && mm) ? task->stack_start : 0,
+ (permitted && mm) ? mm->start_stack : 0,
esp,
eip,
/* The signal information here is obsolete.
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -243,25 +243,6 @@ static void show_map_vma(struct seq_file
} else if (vma->vm_start <= mm->start_stack &&
vma->vm_end >= mm->start_stack) {
name = "[stack]";
- } else {
- unsigned 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,
- "[threadstack:%08lx]",
-#ifdef CONFIG_STACK_GROWSUP
- vma->vm_end - stack_start
-#else
- stack_start - vma->vm_start
-#endif
- );
- }
}
} else {
name = "[vdso]";
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1560,7 +1560,6 @@ struct task_struct {
/* bitmask of trace recursion */
unsigned long trace_recursion;
#endif /* CONFIG_TRACING */
- unsigned long stack_start;
#ifdef CONFIG_CGROUP_MEM_RES_CTLR /* memcg uses this to do batch job */
struct memcg_batch_info {
int do_batch; /* incremented when batch uncharge started */
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1134,8 +1134,6 @@ static struct task_struct *copy_process(

p->bts = NULL;

- p->stack_start = stack_start;
-
/* Perform scheduler related setup. Assign this task to a CPU. */
sched_fork(p, clone_flags);




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