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

sukadev
2007-07-25T19:14:20Z

Pavel Emelianov [xemul@openvz.org] wrote:
| 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...

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.

Suka