Re: [patch 2/2] clone: prepare to recycle CLONE_DETACHED and CLONE_STOPPED

[Andrew Morton <akpm@linux-foundation.org>]

> On Thu, 08 Nov 2007 13:31:43 -0800 akpm@linux-foundation.org wrote:
> From: Andrew Morton <akpm@linux-foundation.org>
> 
> Ulrich says that we never used these clone flags and that nothing should be
> using them.
> 
> As we're down to only a single bit left in clone's flags argument, let's add a
> warning to check that no userspace is actually using these.  Hopefully we will
> be able to recycle them.
> 
> Cc: Ulrich Drepper <drepper@redhat.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Roland McGrath <roland@redhat.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  kernel/fork.c |   16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff -puN kernel/fork.c~clone-prepare-to-recycle-clone_detached-and-clone_stopped kernel/fork.c
> --- a/kernel/fork.c~clone-prepare-to-recycle-clone_detached-and-clone_stopped
> +++ a/kernel/fork.c
> @@ -1420,10 +1420,18 @@ long do_fork(unsigned long clone_flags,
>  	int trace = 0;
>  	long nr;
>  
> -	if (unlikely(current->ptrace)) {
> -		trace = fork_traceflag (clone_flags);
> -		if (trace)
> -			clone_flags |= CLONE_PTRACE;
> +	/*
> +	 * We hope to recycle these flags after 2.6.26
> +	 */
> +	if (unlikely(clone_flags & (CLONE_DETACHED|CLONE_STOPPED))) {
> +		if (printk_ratelimit()) {
> +			char comm[TASK_COMM_LEN];
> +
> +			printk(KERN_INFO "fork(): process `%s' used deprecated "
> +					"clone flags 0x%lx\n",
> +				get_task_comm(comm, current),
> +				clone_flags & (CLONE_DETACHED|CLONE_STOPPED));
> +		}
>  	}
>  
>  	p = copy_process(clone_flags, stack_start, regs, stack_size,

That was all screwed up.  Better version:

From: Andrew Morton <akpm@linux-foundation.org>

Ulrich says that we never used these clone flags and that nothing should be
using them.

As we're down to only a single bit left in clone's flags argument, let's add a
warning to check that no userspace is actually using these.  Hopefully we will
be able to recycle them.

Roland said:

  CLONE_STOPPED was previously used by some NTPL versions when under
  thread_db (i.e.  only when being actively debugged by gdb), but not for a
  long time now, and it never worked reliably when it was used.  Removing it
  seems fine to me.

Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/fork.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff -puN kernel/fork.c~clone-prepare-to-recycle-clone_detached-and-clone_stopped kernel/fork.c
--- a/kernel/fork.c~clone-prepare-to-recycle-clone_detached-and-clone_stopped
+++ a/kernel/fork.c
@@ -1420,6 +1420,23 @@ long do_fork(unsigned long clone_flags,
 	int trace = 0;
 	long nr;
 
+	/*
+	 * We hope to recycle these flags after 2.6.26
+	 */
+	if (unlikely(clone_flags & (CLONE_DETACHED|CLONE_STOPPED))) {
+		static int __read_mostly count = 100;
+
+		if (count && printk_ratelimit()) {
+			char comm[TASK_COMM_LEN];
+
+			count--;
+			printk(KERN_INFO "fork(): process `%s' used deprecated "
+					"clone flags 0x%lx\n",
+				get_task_comm(comm, current),
+				clone_flags & (CLONE_DETACHED|CLONE_STOPPED));
+		}
+	}
+
 	if (unlikely(current->ptrace)) {
 		trace = fork_traceflag (clone_flags);
 		if (trace)
_