[Devel] Re: [RFC][PATCH 2/7] Have alloc_pidmap() return actual error code

[Matt Helsley]

On Mon, May 04, 2009 at 01:17:40AM -0700, sukadev at linux.vnet.ibm.com wrote:
> From: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
> 
> alloc_pidmap() can fail either because all pid numbers are in use or
> we can't allocate memory. With support for setting a specific pid
> number, alloc_pidmap() would also fail if either the given pid
> number is invalid or in use.
> 
> Rather than have caller assume -ENOMEM, have alloc_pidmap() return
> the actual error.

I think generating actual "errors" should be moved into alloc_pidmap_page().

> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
> ---
>  kernel/fork.c |    5 +++--
>  kernel/pid.c  |    9 ++++++---
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index b9e2edd..f8411a8 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1119,10 +1119,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  		goto bad_fork_cleanup_io;
> 
>  	if (pid != &init_struct_pid) {
> -		retval = -ENOMEM;
>  		pid = alloc_pid(p->nsproxy->pid_ns);
> -		if (!pid)
> +		if (IS_ERR(pid)) {
> +			retval = PTR_ERR(pid);
>  			goto bad_fork_cleanup_io;
> +		}
> 
>  		if (clone_flags & CLONE_NEWPID) {
>  			retval = pid_ns_prepare_proc(p->nsproxy->pid_ns);
> diff --git a/kernel/pid.c b/kernel/pid.c
> index c0aaebe..fd72ad9 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -151,6 +151,7 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
>  {
>  	int i, offset, max_scan, pid, last = pid_ns->last_pid;
>  	struct pidmap *map;
> +	int rc = -EAGAIN;
> 
>  	pid = last + 1;
>  	if (pid >= pid_max)
> @@ -159,8 +160,10 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
>  	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
>  	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
>  	for (i = 0; i <= max_scan; ++i) {
> -		if (alloc_pidmap_page(map))
> +		if (alloc_pidmap_page(map)) {
> +			rc = -ENOMEM;

You could return -ENOMEM from alloc_pidmap_page(map) and then just:

	rc = alloc_pidmap_page(map);
	if (rc)
		break;

ENOMEM here is not necessarily correct -- you could have alloc'd pages just fine
and failed due to the last race-checking if () in alloc_pidmap_page(). All the
more reason to move generation of the error to alloc_pidmap_page() IMHO.

Cheers,
	-Matt Helsley
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