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    SubjectRe: [PATCH 13/16] Switch to operating with pid_numbers instead of pids
    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
    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 ?
    -
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