Re: 8139too: defunct threads

Re: 8139too: defunct threads

[Manfred Spraul]

[-- Attachment #1: Type: text/plain, Size: 846 bytes --]

>> Ah. Of course. All (or most) kernel initialisation is
>> done by PID 1. Search for "kernel_thread" in init/main.c
>>
>> So it seems that in your setup, process 1 is not reaping
>> children, which is why this hasn't been reported before.
>> Is there something unusual about your setup?

> I found the difference which causes this. If I build my kernel with
> IP_PNP (IP: kernel level autoconfiguration) support I get a defunt
> thread for each 8139too device. If I don't build with IP_PNP
> support I don't get any, defunct ethernet threads.

Does init(8) reap children that died before it was spawned? I assume
that the defunct tasks were there _before_ init was spawned.

Perhaps init() [in linux/init/main.c] should reap all defunct tasks
before the execve("/sbin/init").

I've attached an untested patch, could you try it?

--
    Manfred


[-- Attachment #2: patch-main.dat --]
[-- Type: application/octet-stream, Size: 423 bytes --]

--- main.c	Fri Mar 30 15:42:49 2001
+++ /pub/home/manfred/main.c	Sat Apr 14 15:56:26 2001
@@ -777,6 +777,13 @@
 
 	(void) dup(0);
 	(void) dup(0);
+
+	while (waitpid(-1, (unsigned int *)0, __WALL|WNOHANG) > 0)
+		;
+	spin_lock_irq(&current->sigmask_lock);
+	flush_signals(curtask);
+	recalc_sigpending(curtask);
+	spin_lock_irq(&current->sigmask_lock);
 	
 	/*
 	 * We try each of these until one succeeds.

Re: 8139too: defunct threads

[Rod Stewart]

On Sat, 14 Apr 2001, Manfred Spraul wrote:

> >> Ah. Of course. All (or most) kernel initialisation is
> >> done by PID 1. Search for "kernel_thread" in init/main.c
> >>
> >> So it seems that in your setup, process 1 is not reaping
> >> children, which is why this hasn't been reported before.
> >> Is there something unusual about your setup?
>
> > I found the difference which causes this. If I build my kernel with
> > IP_PNP (IP: kernel level autoconfiguration) support I get a defunt
> > thread for each 8139too device. If I don't build with IP_PNP
> > support I don't get any, defunct ethernet threads.
>
> Does init(8) reap children that died before it was spawned? I assume
> that the defunct tasks were there _before_ init was spawned.
>
> Perhaps init() [in linux/init/main.c] should reap all defunct tasks
> before the execve("/sbin/init").
>
> I've attached an untested patch, could you try it?

Yes, that fixes my problem.  No more defunct eth? processes when IP_PNP is
compiled in.  With the fix you said to the patch; replacing curtask with
current.

Thanks,
-Rms

[PATCH] Re: 8139too: defunct threads

[Manfred Spraul]

[-- Attachment #1: Type: text/plain, Size: 675 bytes --]

Hi Alan,

Rod's init version (from RH 7.0) doesn't reap children that died before
it was started. Is that an init bug or should the kernel reap them
before the execve?
The attached patch reaps all zombies before the execve("/sbin/init").

I also found a bug in kernel/context.c: it doesn't acquire the sigmask
spinlock around the call to recalc_sigpending.

Rod Stewart wrote:
> 
> Yes, that fixes my problem.  No more defunct eth? processes when IP_PNP is
> compiled in.  With the fix you said to the patch; replacing curtask with
> current.
>
Fortunately you don't use SMP - spin_lock_irq();...;spin_lock_irq()
instead of spin_lock_irq();...;spin_unlock_irq();

--
	Manfred

[-- Attachment #2: patch-child --]
[-- Type: text/plain, Size: 915 bytes --]

// $Header$
// Kernel Version:
//  VERSION = 2
//  PATCHLEVEL = 4
//  SUBLEVEL = 3
//  EXTRAVERSION = -ac3
--- 2.4/init/main.c	Sat Apr  7 22:02:27 2001
+++ build-2.4/init/main.c	Sat Apr 14 19:18:34 2001
@@ -883,6 +883,13 @@
 
 	(void) dup(0);
 	(void) dup(0);
+
+	while (waitpid(-1, (unsigned int *)0, __WALL|WNOHANG) > 0)
+		;
+	spin_lock_irq(&current->sigmask_lock);
+	flush_signals(current);
+	recalc_sigpending(current);
+	spin_unlock_irq(&current->sigmask_lock);
 	
 	/*
 	 * We try each of these until one succeeds.
--- 2.4/kernel/context.c	Fri Feb  2 15:20:37 2001
+++ build-2.4/kernel/context.c	Sat Apr 14 19:09:10 2001
@@ -101,8 +101,10 @@
 		if (signal_pending(curtask)) {
 			while (waitpid(-1, (unsigned int *)0, __WALL|WNOHANG) > 0)
 				;
+			spin_lock_irq(&curtask->sigmask_lock);
 			flush_signals(curtask);
 			recalc_sigpending(curtask);
+			spin_unlock_irq(&curtask->sigmask_lock);
 		}
 	}
 }

Re: [PATCH] Re: 8139too: defunct threads

[Alan Cox]

> Rod's init version (from RH 7.0) doesn't reap children that died before
> it was started. Is that an init bug or should the kernel reap them
> before the execve?

I would say thats an init bug

> The attached patch reaps all zombies before the execve("/sbin/init").

That has an implicit race, a zombie can always appear as we are execing init.
I think init wants fixing

Re: [PATCH] Re: 8139too: defunct threads

[Manfred Spraul]

From: "Alan Cox" <alan@lxorguk.ukuu.org.uk>
>
> That has an implicit race, a zombie can always appear as we are
execing init.
> I think init wants fixing
>
Rod, could you boot again with the unpatched kernel and send a sigchild
to init?

#kill -CHLD 1

If I understand the init code correctly the sigchild handler reaps all
zombies, but probably the signal got lost because the children died
before the parent was created ;-)

--
    Manfred

Re: [PATCH] Re: 8139too: defunct threads

[Rod Stewart]

On Sat, 14 Apr 2001, Manfred Spraul wrote:
> From: "Alan Cox" <alan@lxorguk.ukuu.org.uk>
> >
> > That has an implicit race, a zombie can always appear as we are
> execing init.
> > I think init wants fixing
> >
> Rod, could you boot again with the unpatched kernel and send a sigchild
> to init?
>
> #kill -CHLD 1
>
> If I understand the init code correctly the sigchild handler reaps all
> zombies, but probably the signal got lost because the children died
> before the parent was created ;-)

That doesn't 'fix' it.  The thing I find funny is that it only appears
when IP_PNP is compiled in.  It is as if the driver ends up in some weird
state when IP_PNP is used.  According to ps, from my limited
understanding, the thread is stuck in do_exit

[root@stewart-nw34 /root]# ps elaxww|grep eth
  F   UID   PID  PPID PRI  NI   VSZ  RSS WCHAN  STAT TTY  TIME COMMAND
044     0     7     1   9   0     0    0 do_exi Z    ?  0:00 [eth0 <defunct>]
044     0     8     1   9   0     0    0 do_exi Z    ?  0:00 [eth1 <defunct>]
044     0     9     1   9   0     0    0 do_exi Z    ?  0:00 [eth2 <defunct>]
040     0   229     1   9   0     0    0 rtl813 SW   ?  0:00 [eth1]

Thanks for helping with this,
-Rms

[new PATCH] Re: 8139too: defunct threads

[Manfred Spraul]

[-- Attachment #1: Type: text/plain, Size: 801 bytes --]

I found the problem:

* init uses waitpid(-1,,), thus the __WALL flag is not set
* without __WALL, only processes with exit_signal == SIGCHLD are reaped
* it's impossible for user space processes to die with another
exit_signal, forget_original_parent changes the exit_signal back to
SIGCHLD ("We dont want people slaying init"), and init itself doesn't
use clone.
* kernel threads can die with an arbitrary exit_signal.

Alan, which fix would you prefer:
* init could use wait3 and set __WALL.
* all kernel thread users could set SIGCHLD. Some already do that
(__call_usermodehelper).
* the kernel_thread implementations could force the exit signal to
SIGCHLD.

I'd prefer the last version. 
The attached patch is tested with i386. The alpha, parisc and ppc
assember changes are guessed.

--
	Manfred

[-- Attachment #2: patch-child --]
[-- Type: text/plain, Size: 6794 bytes --]

diff -ur 2.4/arch/alpha/kernel/entry.S build-2.4/arch/alpha/kernel/entry.S
--- 2.4/arch/alpha/kernel/entry.S	Sun Sep  3 20:36:45 2000
+++ build-2.4/arch/alpha/kernel/entry.S	Sun Apr 15 14:58:01 2001
@@ -242,12 +242,12 @@
 	subq	$30,4*8,$30
 	stq	$10,16($30)
 	stq	$9,8($30)
-	lda	$0,CLONE_VM
+	lda	$0,CLONE_VM|SIGCHLD
 	stq	$26,0($30)
 	.prologue 1
 	mov	$16,$9		/* save fn */		
 	mov	$17,$10		/* save arg */
-	or	$18,$0,$16	/* shuffle flags to front; add CLONE_VM.  */
+	or	$18,$0,$16	/* shuffle flags to front; add CLONE_VM|SIGCHLD. */
 	bsr	$26,kernel_clone
 	bne	$20,1f		/* $20 is non-zero in child */
 	ldq	$26,0($30)
diff -ur 2.4/arch/arm/kernel/process.c build-2.4/arch/arm/kernel/process.c
--- 2.4/arch/arm/kernel/process.c	Thu Feb 22 22:28:51 2001
+++ build-2.4/arch/arm/kernel/process.c	Sun Apr 15 14:51:08 2001
@@ -368,6 +368,8 @@
 {
 	pid_t __ret;
 
+	flags |= SIGCHLD;
+
 	__asm__ __volatile__(
 	"orr	r0, %1, %2	@ kernel_thread sys_clone
 	mov	r1, #0
diff -ur 2.4/arch/cris/kernel/process.c build-2.4/arch/cris/kernel/process.c
--- 2.4/arch/cris/kernel/process.c	Sat Apr  7 22:01:49 2001
+++ build-2.4/arch/cris/kernel/process.c	Sun Apr 15 14:51:16 2001
@@ -127,6 +127,8 @@
 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 {
 	register long __a __asm__ ("r10");
+
+	flags |= SIGCHLD;
 	
 	__asm__ __volatile__
 		("movu.w %1,r9\n\t"     /* r9 contains syscall number, to sys_clone */
diff -ur 2.4/arch/i386/kernel/process.c build-2.4/arch/i386/kernel/process.c
--- 2.4/arch/i386/kernel/process.c	Thu Feb 22 22:28:52 2001
+++ build-2.4/arch/i386/kernel/process.c	Sun Apr 15 14:40:43 2001
@@ -440,6 +440,8 @@
 {
 	long retval, d0;
 
+	flags |= SIGCHLD;
+
 	__asm__ __volatile__(
 		"movl %%esp,%%esi\n\t"
 		"int $0x80\n\t"		/* Linux/i386 system call */
diff -ur 2.4/arch/ia64/kernel/process.c build-2.4/arch/ia64/kernel/process.c
--- 2.4/arch/ia64/kernel/process.c	Thu Jan  4 21:50:17 2001
+++ build-2.4/arch/ia64/kernel/process.c	Sun Apr 15 14:51:44 2001
@@ -500,7 +500,7 @@
 	struct task_struct *parent = current;
 	int result, tid;
 
-	tid = clone(flags | CLONE_VM, 0);
+	tid = clone(flags | CLONE_VM | SIGCHLD, 0);
 	if (parent != current) {
 		result = (*fn)(arg);
 		_exit(result);
diff -ur 2.4/arch/m68k/kernel/process.c build-2.4/arch/m68k/kernel/process.c
--- 2.4/arch/m68k/kernel/process.c	Thu Feb 22 22:28:54 2001
+++ build-2.4/arch/m68k/kernel/process.c	Sun Apr 15 14:51:58 2001
@@ -135,7 +135,7 @@
 
 	{
 	register long retval __asm__ ("d0");
-	register long clone_arg __asm__ ("d1") = flags | CLONE_VM;
+	register long clone_arg __asm__ ("d1") = flags | CLONE_VM | SIGCHLD;
 
 	__asm__ __volatile__
 	  ("clrl %%d2\n\t"
diff -ur 2.4/arch/mips/kernel/process.c build-2.4/arch/mips/kernel/process.c
--- 2.4/arch/mips/kernel/process.c	Sat Apr  7 22:01:56 2001
+++ build-2.4/arch/mips/kernel/process.c	Sun Apr 15 14:52:12 2001
@@ -161,6 +161,8 @@
 {
 	long retval;
 
+	flags |= SIGCHLD;
+
 	__asm__ __volatile__(
 		".set\tnoreorder\n\t"
 		"move\t$6,$sp\n\t"
diff -ur 2.4/arch/mips64/kernel/process.c build-2.4/arch/mips64/kernel/process.c
--- 2.4/arch/mips64/kernel/process.c	Thu Feb 22 22:28:55 2001
+++ build-2.4/arch/mips64/kernel/process.c	Sun Apr 15 14:52:21 2001
@@ -154,6 +154,8 @@
 {
 	int retval;
 
+	flags |= SIGCHLD;
+
 	__asm__ __volatile__(
 		"move\t$6, $sp\n\t"
 		"move\t$4, %5\n\t"
diff -ur 2.4/arch/parisc/kernel/entry.S build-2.4/arch/parisc/kernel/entry.S
--- 2.4/arch/parisc/kernel/entry.S	Sat Apr  7 22:01:58 2001
+++ build-2.4/arch/parisc/kernel/entry.S	Sun Apr 15 14:56:58 2001
@@ -497,7 +497,7 @@
 #endif
 	STREG	%r26, PT_GR26(%r1)  /* Store function & argument for child */
 	STREG	%r25, PT_GR25(%r1)
-	ldo	CLONE_VM(%r0), %r26   /* Force CLONE_VM since only init_mm */
+	ldo	SIGCHLD|CLONE_VM(%r0), %r26   /* Force CLONE_VM since only init_mm */
 	or	%r26, %r24, %r26      /* will have kernel mappings.	 */
 	copy	%r0, %r25
 	bl	do_fork, %r2
diff -ur 2.4/arch/ppc/kernel/misc.S build-2.4/arch/ppc/kernel/misc.S
--- 2.4/arch/ppc/kernel/misc.S	Sat Apr  7 22:01:59 2001
+++ build-2.4/arch/ppc/kernel/misc.S	Sun Apr 15 14:56:17 2001
@@ -1080,7 +1080,7 @@
  */
 _GLOBAL(kernel_thread)
 	mr	r6,r3		/* function */
-	ori	r3,r5,CLONE_VM	/* flags */
+	ori	r3,r5,CLONE_VM|SIGCHLD	/* flags */
 	li	r0,__NR_clone
 	sc
 	cmpi	0,r3,0		/* parent or child? */
diff -ur 2.4/arch/s390/kernel/process.c build-2.4/arch/s390/kernel/process.c
--- 2.4/arch/s390/kernel/process.c	Thu Feb 22 22:28:57 2001
+++ build-2.4/arch/s390/kernel/process.c	Sun Apr 15 14:52:58 2001
@@ -242,7 +242,7 @@
 
 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 {
-        int clone_arg = flags | CLONE_VM;
+        int clone_arg = flags | CLONE_VM | SIGCHLD;
         int retval;
 
         __asm__ __volatile__(
diff -ur 2.4/arch/s390x/kernel/process.c build-2.4/arch/s390x/kernel/process.c
--- 2.4/arch/s390x/kernel/process.c	Thu Feb 22 22:28:57 2001
+++ build-2.4/arch/s390x/kernel/process.c	Sun Apr 15 14:53:06 2001
@@ -242,7 +242,7 @@
 
 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 {
-        int clone_arg = flags | CLONE_VM;
+        int clone_arg = flags | CLONE_VM | SIGCHLD;
         int retval;
 
         __asm__ __volatile__(
diff -ur 2.4/arch/sh/kernel/process.c build-2.4/arch/sh/kernel/process.c
--- 2.4/arch/sh/kernel/process.c	Thu Feb 22 22:28:57 2001
+++ build-2.4/arch/sh/kernel/process.c	Sun Apr 15 14:53:16 2001
@@ -148,7 +148,7 @@
 {	/* Don't use this in BL=1(cli).  Or else, CPU resets! */
 	register unsigned long __sc0 __asm__ ("r0");
 	register unsigned long __sc3 __asm__ ("r3") = __NR_clone;
-	register unsigned long __sc4 __asm__ ("r4") = (long) flags | CLONE_VM;
+	register unsigned long __sc4 __asm__ ("r4") = (long) flags | CLONE_VM | SIGCHLD;
 	register unsigned long __sc5 __asm__ ("r5") = 0;
 	register unsigned long __sc8 __asm__ ("r8") = (long) arg;
 	register unsigned long __sc9 __asm__ ("r9") = (long) fn;
diff -ur 2.4/arch/sparc/kernel/process.c build-2.4/arch/sparc/kernel/process.c
--- 2.4/arch/sparc/kernel/process.c	Thu Feb 22 22:28:57 2001
+++ build-2.4/arch/sparc/kernel/process.c	Sun Apr 15 14:53:39 2001
@@ -678,6 +678,8 @@
 {
 	long retval;
 
+	flags |= SIGCHLD;
+
 	__asm__ __volatile("mov %4, %%g2\n\t"    /* Set aside fn ptr... */
 			   "mov %5, %%g3\n\t"    /* and arg. */
 			   "mov %1, %%g1\n\t"
diff -ur 2.4/arch/sparc64/kernel/process.c build-2.4/arch/sparc64/kernel/process.c
--- 2.4/arch/sparc64/kernel/process.c	Sat Mar 31 21:47:37 2001
+++ build-2.4/arch/sparc64/kernel/process.c	Sun Apr 15 14:53:49 2001
@@ -647,6 +647,8 @@
 {
 	long retval;
 
+	flags |= SIGCHLD;
+
 	/* If the parent runs before fn(arg) is called by the child,
 	 * the input registers of this function can be clobbered.
 	 * So we stash 'fn' and 'arg' into global registers which

Re: [new PATCH] Re: 8139too: defunct threads

[Rod Stewart]

On Sun, 15 Apr 2001, Manfred Spraul wrote:

> Alan, which fix would you prefer:
> * init could use wait3 and set __WALL.
> * all kernel thread users could set SIGCHLD. Some already do that
> (__call_usermodehelper).
> * the kernel_thread implementations could force the exit signal to
> SIGCHLD.
>
> I'd prefer the last version.
> The attached patch is tested with i386. The alpha, parisc and ppc
> assember changes are guessed.

This patch fixed my problem.

Thanks,
-Rms

Re: [new PATCH] Re: 8139too: defunct threads

[Andrew Morton]

Manfred Spraul wrote:
> 
> I found the problem:
> 
> * init uses waitpid(-1,,), thus the __WALL flag is not set
> * without __WALL, only processes with exit_signal == SIGCHLD are reaped
> * it's impossible for user space processes to die with another
> exit_signal, forget_original_parent changes the exit_signal back to
> SIGCHLD ("We dont want people slaying init"), and init itself doesn't
> use clone.
> * kernel threads can die with an arbitrary exit_signal.

yep

> Alan, which fix would you prefer:
> * init could use wait3 and set __WALL.
> * all kernel thread users could set SIGCHLD. Some already do that
> (__call_usermodehelper).
> * the kernel_thread implementations could force the exit signal to
> SIGCHLD.

* Add SIGCHLD to all the users of kernel_thread(), in the cases
  where the thread can ever exit.

* Add
	if (current->exit_signal == 0)
		current->exit_signal = SIGCHLD;
  to daemonize().

None of these will work.  The problems with globally setting exit_signal
to SIGCHLD are that

a) If the parent does waitpid(pid, status, __WCLONE), the
   waitpid will fail.  request_module() does this.  I don't
   know _why_ it does this.  Maybe it's bogus.  There is no
   explanation.

b) When the kernel thread exits, it will send a SIGCHLD to
   its parent.  But the parent is not necessarily init!  It
   could be a userspace process (in this case, ifconfig).
   The kernel has no business spraying signals out to userspace
   tasks just because they happened to open a network interface.

   And for this reason we can't just go in and change 8139too.c
   to use SIGCHLD.

So it seems that we must reparent the thread to init, and
make sure that it delivers SIGCHLD to init when it exits.

The below patch does this, within daemonize().  But this precise
area was the source of serial screwups when I was doing the
call_usermodehelper() stuff, and I bet this approach will
still have problems.

The exit_files() will take care of releasing things like current->tty
and pwd.  But we still do not know what scheduling priority and policy
we inherited from the userspace parent, nor do we know what signal mask
we have, nor do we know what uid we're running as.  Resource limits.
Capabilties.  CPU mask.  Etcetera, etcetera.  All this stuff comes back
to bite.  Been there, got the scars :)

This is why I believe that kernel daemons should be launched by
keventd.  They belong to the *kernel*, not to userspace parents.



--- linux-2.4.4-pre3/kernel/sched.c	Sun Apr 15 15:34:25 2001
+++ linux-akpm/kernel/sched.c	Sun Apr 15 21:59:26 2001
@@ -1260,32 +1260,53 @@
 /*
  *	Put all the gunge required to become a kernel thread without
  *	attached user resources in one place where it belongs.
+ *
+ * 	Kernel 2.4.4-pre3, andrewm@uow.edu.au: reparent the caller
+ *	to init and set the exit signal to SIGCHLD so the thread
+ *	will be properly reaped if it exits.
  */
 
 void daemonize(void)
 {
 	struct fs_struct *fs;
-
+	struct task_struct *this_task = current;
 
 	/*
 	 * If we were started as result of loading a module, close all of the
 	 * user space pages.  We don't need them, and if we didn't close them
 	 * they would be locked into memory.
 	 */
-	exit_mm(current);
+	exit_mm(this_task);
 
-	current->session = 1;
-	current->pgrp = 1;
+	this_task->session = 1;
+	this_task->pgrp = 1;
 
 	/* Become as one with the init task */
 
-	exit_fs(current);	/* current->fs->count--; */
+	exit_fs(this_task);	/* this_task->fs->count--; */
 	fs = init_task.fs;
-	current->fs = fs;
+	this_task->fs = fs;
 	atomic_inc(&fs->count);
- 	exit_files(current);
-	current->files = init_task.files;
-	atomic_inc(&current->files->count);
+ 	exit_files(this_task);
+	this_task->files = init_task.files;
+	atomic_inc(&this_task->files->count);
+
+	write_lock_irq(&tasklist_lock);
+
+	/* Reparent to init */
+	REMOVE_LINKS(this_task);
+	this_task->p_opptr = child_reaper;
+	this_task->p_pptr = child_reaper;
+	SET_LINKS(this_task);
+
+	/* Set the exit signal to SIGCHLD so we signal init on exit */
+	if (this_task->exit_signal ! 0) {
+		printk(KERN_ERR "task `%s' exit_signal %d in daemonize()\n",
+			this_task->comm, this_task->exit_signal);
+	}
+	this_task->exit_signal = SIGCHLD;
+
+	write_unlock_irq(&tasklist_lock);
 }
 
 void __init init_idle(void)

Re: [new PATCH] Re: 8139too: defunct threads

[John Fremlin]

 Andrew Morton <andrewm@uow.edu.au> writes:

[...]

> None of these will work.  The problems with globally setting
> exit_signal to SIGCHLD are that
> 
> a) If the parent does waitpid(pid, status, __WCLONE), the
>    waitpid will fail.  request_module() does this.  I don't
>    know _why_ it does this.  Maybe it's bogus.  There is no
>    explanation.

waitpid doesn't work on cloned children unless you put in __WCLONE or
__WALL, so this was necessary to catch the child at all. If you set to
use SIGCHLD this will no longer be needed (if I understand correctly).

[...]

> So it seems that we must reparent the thread to init, and
> make sure that it delivers SIGCHLD to init when it exits.

Sounds good. Why isn't SIGCHLD a stronger default anyway.

[...]

> +	/* Set the exit signal to SIGCHLD so we signal init on exit */
> +	if (this_task->exit_signal ! 0) {

Tyop.

> +		printk(KERN_ERR "task `%s' exit_signal %d in daemonize()\n",
> +			this_task->comm, this_task->exit_signal);
> +	}
> +	this_task->exit_signal = SIGCHLD;
> +
> +	write_unlock_irq(&tasklist_lock);
>  }
>  
>  void __init init_idle(void)
> 

-- 

	http://www.penguinpowered.com/~vii

Re: [new PATCH] Re: 8139too: defunct threads

[Andrew Morton]

John Fremlin wrote:
> 
> 
> > So it seems that we must reparent the thread to init, and
> > make sure that it delivers SIGCHLD to init when it exits.
> 
> Sounds good. Why isn't SIGCHLD a stronger default anyway.

mm?   The caller gets to choose...

> [...]
> 
> > +     /* Set the exit signal to SIGCHLD so we signal init on exit */
> > +     if (this_task->exit_signal ! 0) {
> 
> Tyop.

aargh.  Thanks.  So that's what `cvs commit' does :)

The patch is OK with this converted into `!='.  But I'll
refresh and retest for tomorrow.  Still not very happy with
this approach though...

Re: [PATCH] Re: 8139too: defunct threads

[Andreas Ferber]

Hi,

On Sat, Apr 14, 2001 at 07:53:28PM +0100, Alan Cox wrote:
> > Rod's init version (from RH 7.0) doesn't reap children that died before
> > it was started. Is that an init bug or should the kernel reap them
> > before the execve?
> I would say thats an init bug

It doesn't seem to be that simple.

Redhat's init does child reaping in its SIGCHLD handler using the
following:

while((pid = waitpid(-1, &st, WNOHANG)) != 0) {
    if (errno == ECHILD) break;
    /* do some stuff, nothing which could break out of the loop */
}

This should reap all leftover childs from kernel startup when init
receives SIGCHLD for the first time, but somehow the kernel seems to
skip them while searching for a dead process in sys_wait4().  I can't
do any further testing because I don't have a 8139 NIC, but I can't
find a problem in init's child reaping code.

Please tell me if I'm missing something, but I think this is really a
kernel issue, not a bug in init.

Andreas
-- 
I've finally learned what "upward compatible" means.  It means we get to
keep all our old mistakes.
		-- Dennie van Tassel