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SubjectRe: [PATCH 8/9] Call idr_find() without locking in ipc_lock()
On Wed, May 07, 2008 at 01:36:01PM +0200, Nadia.Derbey@bull.net wrote:
> [PATCH 08/09]
>
> This patch makes idr_find() called locklessly in ipc_lock(), since the idr
> tree is now RCU protected.

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
>
> ---
> ipc/util.c | 9 ---------
> 1 file changed, 9 deletions(-)
>
> Index: linux-2.6.25-mm1/ipc/util.c
> ===================================================================
> --- linux-2.6.25-mm1.orig/ipc/util.c 2008-05-06 17:15:10.000000000 +0200
> +++ linux-2.6.25-mm1/ipc/util.c 2008-05-07 09:56:20.000000000 +0200
> @@ -688,10 +688,6 @@ void ipc64_perm_to_ipc_perm (struct ipc6
> * Look for an id in the ipc ids idr and lock the associated ipc object.
> *
> * The ipc object is locked on exit.
> - *
> - * This is the routine that should be called when the rw_mutex is not already
> - * held, i.e. idr tree not protected: it protects the idr tree in read mode
> - * during the idr_find().
> */
>
> struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
> @@ -699,18 +695,13 @@ struct kern_ipc_perm *ipc_lock(struct ip
> struct kern_ipc_perm *out;
> int lid = ipcid_to_idx(id);
>
> - down_read(&ids->rw_mutex);
> -
> rcu_read_lock();
> out = idr_find(&ids->ipcs_idr, lid);
> if (out == NULL) {
> rcu_read_unlock();
> - up_read(&ids->rw_mutex);
> return ERR_PTR(-EINVAL);
> }
>
> - up_read(&ids->rw_mutex);
> -
> spin_lock(&out->lock);
>
> /* ipc_rmid() may have already freed the ID while ipc_lock
>
> --


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