ipc: introduce obtaining a lockless ipc object
Through ipc_lock() and therefore ipc_lock_check() we currently return the
locked ipc object. This is not necessary for all situations and can,
therefore, cause unnecessary ipc lock contention.
Introduce analogous ipc_obtain_object() and ipc_obtain_object_check()
functions that only lookup and return the ipc object.
Both these functions must be called within the RCU read critical section.
[akpm@linux-foundation.org: propagate the ipc_obtain_object() errno from ipc_lock()]
Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Chegu Vinod <chegu_vinod@hp.com>
Acked-by: Michel Lespinasse <walken@google.com>
Cc: Emmanuel Benisty <benisty.e@gmail.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/util.c b/ipc/util.c
index 03eadd8..813804e 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -669,38 +669,81 @@
}
/**
+ * ipc_obtain_object
+ * @ids: ipc identifier set
+ * @id: ipc id to look for
+ *
+ * Look for an id in the ipc ids idr and return associated ipc object.
+ *
+ * Call inside the RCU critical section.
+ * The ipc object is *not* locked on exit.
+ */
+struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id)
+{
+ struct kern_ipc_perm *out;
+ int lid = ipcid_to_idx(id);
+
+ out = idr_find(&ids->ipcs_idr, lid);
+ if (!out)
+ return ERR_PTR(-EINVAL);
+
+ return out;
+}
+
+/**
* ipc_lock - Lock an ipc structure without rw_mutex held
* @ids: IPC identifier set
* @id: ipc id to look for
*
* Look for an id in the ipc ids idr and lock the associated ipc object.
*
- * The ipc object is locked on exit.
+ * The ipc object is locked on successful exit.
*/
-
struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
{
struct kern_ipc_perm *out;
- int lid = ipcid_to_idx(id);
rcu_read_lock();
- out = idr_find(&ids->ipcs_idr, lid);
- if (out == NULL) {
- rcu_read_unlock();
- return ERR_PTR(-EINVAL);
- }
+ out = ipc_obtain_object(ids, id);
+ if (IS_ERR(out))
+ goto err1;
spin_lock(&out->lock);
-
+
/* ipc_rmid() may have already freed the ID while ipc_lock
* was spinning: here verify that the structure is still valid
*/
- if (out->deleted) {
- spin_unlock(&out->lock);
- rcu_read_unlock();
- return ERR_PTR(-EINVAL);
- }
+ if (!out->deleted)
+ return out;
+ spin_unlock(&out->lock);
+ out = ERR_PTR(-EINVAL);
+err1:
+ rcu_read_unlock();
+ return out;
+}
+
+/**
+ * ipc_obtain_object_check
+ * @ids: ipc identifier set
+ * @id: ipc id to look for
+ *
+ * Similar to ipc_obtain_object() but also checks
+ * the ipc object reference counter.
+ *
+ * Call inside the RCU critical section.
+ * The ipc object is *not* locked on exit.
+ */
+struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id)
+{
+ struct kern_ipc_perm *out = ipc_obtain_object(ids, id);
+
+ if (IS_ERR(out))
+ goto out;
+
+ if (ipc_checkid(out, id))
+ return ERR_PTR(-EIDRM);
+out:
return out;
}