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Commit 34441427 authored by Robin Holt's avatar Robin Holt Committed by Linus Torvalds
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revert "procfs: provide stack information for threads" and its fixup commits 



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 9ebd4eba ("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 1306d603 ('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: default avatarRobin 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>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3c904afd

Documentation/filesystems/proc.txt

+1 −2
Original line number Diff line number Diff line
@@ -316,7 +316,7 @@ address perms offset dev inode pathname 
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
@@ -352,7 +352,6 @@ 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.

fs/compat.c

+0 −2
Original line number Diff line number Diff line
@@ -1531,8 +1531,6 @@ 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;

fs/exec.c

+0 −2
Original line number Diff line number Diff line
@@ -1387,8 +1387,6 @@ 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;

fs/proc/array.c

+1 −2
Original line number Diff line number Diff line
@@ -81,7 +81,6 @@ 
#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>
@@ -495,7 +494,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, 
		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.

fs/proc/task_mmu.c

+0 −19
Original line number Diff line number Diff line
@@ -247,25 +247,6 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma) 
				} 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]";