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

[Pavel Emelyanov]

sukadev at us.ibm.com wrote:
> Pavel Emelianov [xemul at openvz.org] wrote:
> | sukadev at us.ibm.com wrote:
> | >Pavel Emelianov [xemul at 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 at 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...
> 
> Aah descending - thats right. But I still think there is a problem.
> 
> Here is your code that I am referring to:
> 
>         pid = kmem_cache_alloc(pid_ns->pid_cachep, GFP_KERNEL);
>         if (!pid)
>                 goto out;
> 
>         ns = pid_ns;
>         for (i = pid_ns->level; i >= 0; i--) {
>                 nr = alloc_pidmap(ns);
>                 if (nr < 0)
>                         goto out_free;
> 
>                 pid->numbers[i].nr = nr;
>                 pid->numbers[i].ns = ns;
>                 ns = ns->parent;
>         }
> 
> 	pid->level = pid_ns->level;
> 
> 	<snip>
> 
> out:
> 	return pid;
> out_free:
>         for (i++; i <= pid->level; i++)
>                 free_pidmap(pid->numbers[i].ns, pid->numbers[i].nr);
> 
>         kmem_cache_free(pid_ns->pid_cachep, pid);
>         pid = NULL;
> 	goto out;
> 
> <end code>
> 
> Lets say initially pid_ns->level = 3 and alloc_pidmap() succeeds for
> i=3 and i=2 but fails for i=1 and we execute "goto out_free".
> 
> But pid->level is uninitialized at this point right ?
> 
> Even if it were set to zero (using kmem_cache_zalloc()), we may not
> free the two pidmap entries we allocated for i=3 and i=2.

Yes. I found this after detailed look at the code and (hope) fixed.

> Suka
> 

Thanks,
Pavel

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