This is an updated version of Eric Biederman's is_init() patch.
(http://lkml.org/lkml/2006/2/6/280). It applies cleanly to 2.6.18-rc2
and replaces a few more instances of ->pid == 1 with is_init().

Further, is_init() checks pid and thus removes dependency on Eric's
other patches for now.

Couple of questions:

	Are there cases where child_reaper is not pid = 1. Should the
	"tsk == child_reaper" check in do_exit() be replaced with is_init() ? 

	Looks like, we would need a similar, is_idle() wrapper for "pid==0"
	checks - although the name is_idle_task() maybe more intuitive. If
	so, should we rename is_init() to is_init_task() ? 


Eric's original description: 

	There are a lot of places in the kernel where we test for init
	because we give it special properties.  Most  significantly init
	must not die.  This results in code all over the kernel test
	->pid == 1.

	Introduce is_init to capture this case.  

	With multiple pid spaces for all of the cases affected we are
	looking for only the first process on the system, not some other
	process that has pid == 1. 

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: lxc-devel@lists.sourceforge.net


 arch/alpha/mm/fault.c                |    2 +-
 arch/arm/mm/fault.c                  |    2 +-
 arch/arm26/mm/fault.c                |    2 +-
 arch/i386/lib/usercopy.c             |    2 +-
 arch/i386/mm/fault.c                 |    2 +-
 arch/ia64/mm/fault.c                 |    2 +-
 arch/m32r/mm/fault.c                 |    2 +-
 arch/m68k/mm/fault.c                 |    2 +-
 arch/mips/mm/fault.c                 |    2 +-
 arch/powerpc/mm/fault.c              |    2 +-
 arch/powerpc/platforms/pseries/ras.c |    2 +-
 arch/ppc/kernel/traps.c              |    2 +-
 arch/ppc/mm/fault.c                  |    2 +-
 arch/s390/mm/fault.c                 |    2 +-
 arch/sh/mm/fault.c                   |    2 +-
 arch/sh64/mm/fault.c                 |    6 +++---
 arch/um/kernel/trap.c                |    2 +-
 arch/x86_64/mm/fault.c               |    4 ++--
 arch/xtensa/mm/fault.c               |    2 +-
 drivers/char/sysrq.c                 |    2 +-
 include/linux/sched.h                |   10 ++++++++++
 kernel/capability.c                  |    2 +-
 kernel/cpuset.c                      |    2 +-
 kernel/exit.c                        |    2 +-
 kernel/kexec.c                       |    2 +-
 kernel/ptrace.c                      |    1 +
 kernel/sysctl.c                      |    2 +-
 mm/oom_kill.c                        |    6 +++---
 security/commoncap.c                 |    2 +-
 security/seclvl.c                    |    9 +++++----
 30 files changed, 48 insertions(+), 36 deletions(-)

Index: linux-2.6.18-rc2c/arch/alpha/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/alpha/mm/fault.c	2006-07-28 09:20:03.000000000 -0700
+++ linux-2.6.18-rc2c/arch/alpha/mm/fault.c	2006-07-28 09:35:37.000000000 -0700
@@ -193,7 +193,7 @@ do_page_fault(unsigned long address, uns
 	/* We ran out of memory, or some other thing happened to us that
 	   made us unable to handle the page fault gracefully.  */
  out_of_memory:
-	if (current->pid == 1) {
+	if (is_init(current)) {
 		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
Index: linux-2.6.18-rc2c/arch/arm/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/arm/mm/fault.c	2006-07-28 09:20:04.000000000 -0700
+++ linux-2.6.18-rc2c/arch/arm/mm/fault.c	2006-07-31 17:53:40.000000000 -0700
@@ -197,7 +197,7 @@ survive:
 		return fault;
 	}
 
-	if (tsk->pid != 1)
+	if (!is_init(tsk))
 		goto out;
 
 	/*
Index: linux-2.6.18-rc2c/arch/arm26/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/arm26/mm/fault.c	2006-07-28 09:19:59.000000000 -0700
+++ linux-2.6.18-rc2c/arch/arm26/mm/fault.c	2006-07-31 22:48:32.000000000 -0700
@@ -185,7 +185,7 @@ survive:
 	}
 
 	fault = -3; /* out of memory */
-	if (tsk->pid != 1)
+	if (!is_init(tsk))
 		goto out;
 
 	/*
Index: linux-2.6.18-rc2c/arch/i386/lib/usercopy.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/i386/lib/usercopy.c	2006-07-28 09:19:49.000000000 -0700
+++ linux-2.6.18-rc2c/arch/i386/lib/usercopy.c	2006-07-28 09:35:37.000000000 -0700
@@ -739,7 +739,7 @@ survive:
 			retval = get_user_pages(current, current->mm,
 					(unsigned long )to, 1, 1, 0, &pg, NULL);
 
-			if (retval == -ENOMEM && current->pid == 1) {
+			if (retval == -ENOMEM && is_init(current)) {
 				up_read(&current->mm->mmap_sem);
 				blk_congestion_wait(WRITE, HZ/50);
 				goto survive;
Index: linux-2.6.18-rc2c/arch/i386/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/i386/mm/fault.c	2006-07-28 09:19:49.000000000 -0700
+++ linux-2.6.18-rc2c/arch/i386/mm/fault.c	2006-07-28 09:35:37.000000000 -0700
@@ -598,7 +598,7 @@ no_context:
  */
 out_of_memory:
 	up_read(&mm->mmap_sem);
-	if (tsk->pid == 1) {
+	if (is_init(tsk)) {
 		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
Index: linux-2.6.18-rc2c/arch/ia64/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/ia64/mm/fault.c	2006-07-28 09:20:02.000000000 -0700
+++ linux-2.6.18-rc2c/arch/ia64/mm/fault.c	2006-07-28 09:35:37.000000000 -0700
@@ -278,7 +278,7 @@ ia64_do_page_fault (unsigned long addres
 
   out_of_memory:
 	up_read(&mm->mmap_sem);
-	if (current->pid == 1) {
+	if (is_init(current)) {
 		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
Index: linux-2.6.18-rc2c/arch/m32r/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/m32r/mm/fault.c	2006-07-28 09:20:09.000000000 -0700
+++ linux-2.6.18-rc2c/arch/m32r/mm/fault.c	2006-07-28 09:35:37.000000000 -0700
@@ -299,7 +299,7 @@ no_context:
  */
 out_of_memory:
 	up_read(&mm->mmap_sem);
-	if (tsk->pid == 1) {
+	if (is_init(tsk)) {
 		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
Index: linux-2.6.18-rc2c/arch/m68k/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/m68k/mm/fault.c	2006-07-28 09:20:00.000000000 -0700
+++ linux-2.6.18-rc2c/arch/m68k/mm/fault.c	2006-07-28 09:35:37.000000000 -0700
@@ -181,7 +181,7 @@ good_area:
  */
 out_of_memory:
 	up_read(&mm->mmap_sem);
-	if (current->pid == 1) {
+	if (is_init(current)) {
 		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
Index: linux-2.6.18-rc2c/arch/mips/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/mips/mm/fault.c	2006-07-28 09:19:54.000000000 -0700
+++ linux-2.6.18-rc2c/arch/mips/mm/fault.c	2006-07-28 09:35:37.000000000 -0700
@@ -171,7 +171,7 @@ no_context:
  */
 out_of_memory:
 	up_read(&mm->mmap_sem);
-	if (tsk->pid == 1) {
+	if (is_init(tsk)) {
 		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
Index: linux-2.6.18-rc2c/arch/powerpc/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/powerpc/mm/fault.c	2006-07-28 09:20:10.000000000 -0700
+++ linux-2.6.18-rc2c/arch/powerpc/mm/fault.c	2006-07-28 09:35:37.000000000 -0700
@@ -386,7 +386,7 @@ bad_area_nosemaphore:
  */
 out_of_memory:
 	up_read(&mm->mmap_sem);
-	if (current->pid == 1) {
+	if (is_init(current)) {
 		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
Index: linux-2.6.18-rc2c/arch/powerpc/platforms/pseries/ras.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/powerpc/platforms/pseries/ras.c	2006-07-28 09:20:10.000000000 -0700
+++ linux-2.6.18-rc2c/arch/powerpc/platforms/pseries/ras.c	2006-07-28 09:35:37.000000000 -0700
@@ -337,7 +337,7 @@ static int recover_mce(struct pt_regs *r
 		   err->disposition == RTAS_DISP_NOT_RECOVERED &&
 		   err->target == RTAS_TARGET_MEMORY &&
 		   err->type == RTAS_TYPE_ECC_UNCORR &&
-		   !(current->pid == 0 || current->pid == 1)) {
+		   !(current->pid == 0 || is_init(current))) {
 		/* Kill off a user process with an ECC error */
 		printk(KERN_ERR "MCE: uncorrectable ecc error for pid %d\n",
 		       current->pid);
Index: linux-2.6.18-rc2c/arch/ppc/kernel/traps.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/ppc/kernel/traps.c	2006-07-28 09:19:52.000000000 -0700
+++ linux-2.6.18-rc2c/arch/ppc/kernel/traps.c	2006-07-28 13:10:05.000000000 -0700
@@ -119,7 +119,7 @@ void _exception(int signr, struct pt_reg
 	 * generate the same exception over and over again and we get
 	 * nowhere.  Better to kill it and let the kernel panic.
 	 */
-	if (current->pid == 1) {
+	if (is_init(current)) {
 		__sighandler_t handler;
 
 		spin_lock_irq(&current->sighand->siglock);
Index: linux-2.6.18-rc2c/arch/ppc/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/ppc/mm/fault.c	2006-07-28 09:19:51.000000000 -0700
+++ linux-2.6.18-rc2c/arch/ppc/mm/fault.c	2006-07-28 13:11:06.000000000 -0700
@@ -291,7 +291,7 @@ bad_area:
  */
 out_of_memory:
 	up_read(&mm->mmap_sem);
-	if (current->pid == 1) {
+	if (is_init(current)) {
 		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
Index: linux-2.6.18-rc2c/arch/s390/mm/fault.c
===================================================================
--- linux-2.6.18-rc2c.orig/arch/s390/mm/fault.c	2006-07-28 09:20

Sukadev Bhattiprolu <sukadev@us.ibm.com> writes:

> This is an updated version of Eric Biederman's is_init() patch.
> (http://lkml.org/lkml/2006/2/6/280). It applies cleanly to 2.6.18-rc2
> and replaces a few more instances of ->pid == 1 with is_init().
>
> Further, is_init() checks pid and thus removes dependency on Eric's
> other patches for now.

Sorry for the delay.  I've been catching up on other things before
I dived back in.

> Couple of questions:
>
> 	Are there cases where child_reaper is not pid = 1. Should the
> 	"tsk == child_reaper" check in do_exit() be replaced with is_init() ? 

There are cases where there are multiple child_reapers.
So is_init() is not the right test there.

There is a really weird case when you have a threaded init and the primary
thread exits where things get weird.  As I recall there wind up being two
tasks with tgid == 1 and pid == 1.  So simply testing the pid is not
sufficient.

> 	Looks like, we would need a similar, is_idle() wrapper for "pid==0"
> 	checks - although the name is_idle_task() maybe more intuitive. If
> 	so, should we rename is_init() to is_init_task() ? 

Whatever works.  I'm not too particular as long as the important bits happen.
However pid == 0 only ever lives in the root pspace and never shows up in
the pid hash tables so we can get away without a special check.

Eric

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