| Re: [PATCH] Reduce uidhash lock hold time when lookup succeeds [message #41775 is a reply to message #41762] |
Fri, 18 February 2011 18:25  |
Serge E. Hallyn
Messages: 26
Registered: February 2011
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Junior Member |
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Quoting Matt Helsley (matthltc@us.ibm.com):
> When lookup succeeds we don't need the "new" user struct which hasn't
> been linked into the uidhash. So we can immediately drop the lock and
> then free "new" rather than free it with the lock held.
>
> Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
> Cc: David Howells <dhowells@redhat.com>
> Cc: Pavel Emelyanov <xemul@parallels.com>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: "Serge E. Hallyn" <serge@hallyn.com>
Acked-by: Serge E. Hallyn <serge@hallyn.com>
And might I say that the label 'out_unlock' in that function is
sadly named :)
> Cc: containers@lists.linux-foundation.org
> ---
> kernel/user.c | 12 +++++++-----
> 1 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/user.c b/kernel/user.c
> index 5c598ca..4ea8e58 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -157,16 +157,18 @@ struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
> */
> spin_lock_irq(&uidhash_lock);
> up = uid_hash_find(uid, hashent);
> - if (up) {
> + if (!up) {
> + uid_hash_insert(new, hashent);
> + up = new;
> + }
> + spin_unlock_irq(&uidhash_lock);
> +
> + if (up != new) {
> put_user_ns(ns);
> key_put(new->uid_keyring);
> key_put(new->session_keyring);
> kmem_cache_free(uid_cachep, new);
> - } else {
> - uid_hash_insert(new, hashent);
> - up = new;
> }
> - spin_unlock_irq(&uidhash_lock);
> }
>
> return up;
> --
> 1.6.3.3
>
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/containe rs
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