Re: [PATCH 13/16] Switch to operating with pid_numbers instead of pids

[Pavel Emelyanov <xemul@openvz.org>]

sukadev@us.ibm.com wrote:
> Pavel Emelianov [xemul@openvz.org] wrote:
> | Make alloc_pid() initialize pid_numbers and hash them
> | into the hashtable, not the struct pid itself.
> | 
> | Signed-off-by: Pavel Emelianov <xemul@openvz.org>
> | 
> | ---
> | 
> |  pid.c |   47 +++++++++++++++++++++++++++++++++--------------
> |  1 files changed, 33 insertions(+), 14 deletions(-)
> | 
> | --- ./kernel/pid.c.ve12	2007-07-05 11:06:41.000000000 +0400
> | +++ ./kernel/pid.c	2007-07-05 11:08:23.000000000 +0400
> | @@ -28,8 +28,10 @@
> |  #include <linux/hash.h>
> |  #include <linux/pid_namespace.h>
> |  #include <linux/init_task.h>
> | +#include <linux/proc_fs.h>
> | 
> | -#define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
> | +#define pid_hashfn(nr, ns)	\
> | +	hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
> |  static struct hlist_head *pid_hash;
> |  static int pidhash_shift;
> |  struct pid init_struct_pid = INIT_STRUCT_PID;
> | @@ -194,7 +198,7 @@ fastcall void put_pid(struct pid *pid)
> |  	if (!pid)
> |  		return;
> | 
> | -	ns = pid->numbers[0].ns;
> | +	ns = pid->numbers[pid->level].ns;
> |  	if ((atomic_read(&pid->count) == 1) ||
> |  	     atomic_dec_and_test(&pid->count))
> |  		kmem_cache_free(ns->pid_cachep, pid);
> | @@ -210,13 +214,17 @@ static void delayed_put_pid(struct rcu_h
> |  fastcall void free_pid(struct pid *pid)
> |  {
> |  	/* We can be called with write_lock_irq(&tasklist_lock) held */
> | +	int i;
> |  	unsigned long flags;
> | 
> |  	spin_lock_irqsave(&pidmap_lock, flags);
> | -	hlist_del_rcu(&pid->pid_chain);
> | +	for (i = 0; i <= pid->level; i++)
> | +		hlist_del_rcu(&pid->numbers[i].pid_chain);
> |  	spin_unlock_irqrestore(&pidmap_lock, flags);
> | 
> | -	free_pidmap(&init_pid_ns, pid->nr);
> | +	for (i = 0; i <= pid->level; i++)
> | +		free_pidmap(pid->numbers[i].ns, pid->numbers[i].nr);
> | +
> |  	call_rcu(&pid->rcu, delayed_put_pid);
> |  }
> | 
> | @@ -224,30 +232,43 @@ struct pid *alloc_pid(struct pid_namespa
> |  {
> |  	struct pid *pid;
> |  	enum pid_type type;
> | -	int nr = -1;
> | +	struct pid_namespace *ns;
> | +	int i, nr;
> | 
> | -	pid = kmem_cache_alloc(init_pid_ns.pid_cachep, GFP_KERNEL);
> | +	pid = kmem_cache_alloc(pid_ns->pid_cachep, GFP_KERNEL);
> |  	if (!pid)
> |  		goto out;
> | 
> | -	nr = alloc_pidmap(current->nsproxy->pid_ns);
> | -	if (nr < 0)
> | -		goto out_free;
> | +	ns = pid_ns;
> | +	for (i = pid_ns->level; i >= 0; i--) {
> | +		nr = alloc_pidmap(ns);
> | +		if (nr < 0)
> | +			goto out_free;
> 
> If pid_ns->level is say 3 and alloc_pidmap() succeeds when i=0,1

It cannot :) If level is 3, then we'll allocate for 3, 2, 1, 0 sequence.
The loop is descending, not ascending...

> and fails when i=2, we would try to free_pidmap() even from 
> pid->pid_number[2].pid_ns. This would incorrectly a)
> drop reference count on that pid namespace, and incorrectly
> increment pidmap->nr_free.
> 
> Should we use kmem_cache_zalloc() and check for a non-NULL pid_ns
> before calling free_pidmap() below ?
> 
> | 
> | +		pid->numbers[i].nr = nr;
> | +		pid->numbers[i].ns = ns;
> | +		ns = ns->parent;
> | +	}
> | +
> | +	pid->level = pid_ns->level;
> |  	atomic_set(&pid->count, 1);
> | -	pid->nr = nr;
> |  	for (type = 0; type < PIDTYPE_MAX; ++type)
> |  		INIT_HLIST_HEAD(&pid->tasks[type]);
> | 
> |  	spin_lock_irq(&pidmap_lock);
> | -	hlist_add_head_rcu(&pid->pid_chain, &pid_hash[pid_hashfn(pid->nr)]);
> | +	for (i = pid->level; i >= 0; i--)
> | +		hlist_add_head_rcu(&pid->numbers[i].pid_chain,
> | +				&pid_hash[pid_hashfn(pid->numbers[i].nr,
> | +					pid->numbers[i].ns)]);
> |  	spin_unlock_irq(&pidmap_lock);
> | -
> |  out:
> |  	return pid;
> | 
> |  out_free:
> | -	kmem_cache_free(init_pid_ns.pid_cachep, pid);
> | +	for (i++; i <= pid->level; i++)
> | +		free_pidmap(pid->numbers[i].ns, pid->numbers[i].nr);
> 
> i.e all pid->numbers[] may not be initialized here right ?

The numbers from i up to pid->level are initialized, so this
loop looks correct.

Thanks,
Pavel