sysvipc: unteach ids->next_id for !CHECKPOINT_RESTORE

Patch series "sysvipc: ipc-key management improvements".

Here are a few improvements I spotted while eyeballing Guillaume's
rhashtable implementation for ipc keys.  The first and fourth patches
are the interesting ones, the middle two are trivial.

This patch (of 4):

The next_id object-allocation functionality was introduced in commit
03f595668017 ("ipc: add sysctl to specify desired next object id").

Given that these new entries are _only_ exported under the
CONFIG_CHECKPOINT_RESTORE option, there is no point for the common case
to even know about ->next_id.  As such rewrite ipc_buildid() such that
it can do away with the field as well as unnecessary branches when
adding a new identifier.  The end result also better differentiates both
cases, so the code ends up being cleaner; albeit the small duplications
regarding the default case.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170831172049.14576-2-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 45 insertions, 20 deletions

diff --git a/ipc/util.c b/ipc/util.c
index 79b30eee32cd..429c06bdb8ef 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -116,13 +116,15 @@ int ipc_init_ids(struct ipc_ids *ids)
         int err;
         ids->in_use = 0;
         ids->seq = 0;
-        ids->next_id = -1;
         init_rwsem(&ids->rwsem);
         err = rhashtable_init(&ids->key_ht, &ipc_kht_params);
         if (err)
                 return err;
         idr_init(&ids->ipcs_idr);
         ids->tables_initialized = true;
+#ifdef CONFIG_CHECKPOINT_RESTORE
+        ids->next_id = -1;
+#endif
         return 0;
 }
 
@@ -216,6 +218,46 @@ int ipc_get_maxid(struct ipc_ids *ids)
         return max_id;
 }
 
+#ifdef CONFIG_CHECKPOINT_RESTORE
+/*
+ * Specify desired id for next allocated IPC object.
+ */
+#define ipc_idr_alloc(ids, new)                                         \
+        idr_alloc(&(ids)->ipcs_idr, (new),                              \
+                  (ids)->next_id < 0 ? 0 : ipcid_to_idx((ids)->next_id),\
+                  0, GFP_NOWAIT)
+
+static inline int ipc_buildid(int id, struct ipc_ids *ids,
+                              struct kern_ipc_perm *new)
+{
+        if (ids->next_id < 0) { /* default, behave as !CHECKPOINT_RESTORE */
+                new->seq = ids->seq++;
+                if (ids->seq > IPCID_SEQ_MAX)
+                        ids->seq = 0;
+        } else {
+                new->seq = ipcid_to_seqx(ids->next_id);
+                ids->next_id = -1;
+        }
+
+        return SEQ_MULTIPLIER * new->seq + id;
+}
+
+#else
+#define ipc_idr_alloc(ids, new)                                 \
+        idr_alloc(&(ids)->ipcs_idr, (new), 0, 0, GFP_NOWAIT)
+
+static inline int ipc_buildid(int id, struct ipc_ids *ids,
+                              struct kern_ipc_perm *new)
+{
+        new->seq = ids->seq++;
+        if (ids->seq > IPCID_SEQ_MAX)
+                ids->seq = 0;
+
+        return SEQ_MULTIPLIER * new->seq + id;
+}
+
+#endif /* CONFIG_CHECKPOINT_RESTORE */
+
 /**
  * ipc_addid - add an ipc identifier
  * @ids: ipc identifier set
@@ -234,7 +276,6 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)
         kuid_t euid;
         kgid_t egid;
         int id, err;
-        int next_id = ids->next_id;
 
         if (size > IPCMNI)
                 size = IPCMNI;
@@ -254,9 +295,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)
         new->cuid = new->uid = euid;
         new->gid = new->cgid = egid;
 
-        id = idr_alloc(&ids->ipcs_idr, new,
-                       (next_id < 0) ? 0 : ipcid_to_idx(next_id), 0,
-                       GFP_NOWAIT);
+        id = ipc_idr_alloc(ids, new);
         idr_preload_end();
 
         if (id >= 0 && new->key != IPC_PRIVATE) {
@@ -274,17 +313,8 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)
         }
 
         ids->in_use++;
+        new->id = ipc_buildid(id, ids, new);
 
-        if (next_id < 0) {
-                new->seq = ids->seq++;
-                if (ids->seq > IPCID_SEQ_MAX)
-                        ids->seq = 0;
-        } else {
-                new->seq = ipcid_to_seqx(next_id);
-                ids->next_id = -1;
-        }
-
-        new->id = ipc_buildid(id, new->seq);
         return id;
 }
 
diff --git a/ipc/util.h b/ipc/util.h
index 579112d90016..0cd6201fe63a 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -146,11 +146,6 @@ extern struct msg_msg *load_msg(const void __user *src, size_t len);
 extern struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst);
 extern int store_msg(void __user *dest, struct msg_msg *msg, size_t len);
 
-static inline int ipc_buildid(int id, int seq)
-{
-        return SEQ_MULTIPLIER * seq + id;
-}
-
 static inline int ipc_checkid(struct kern_ipc_perm *ipcp, int uid)
 {
         return uid / SEQ_MULTIPLIER != ipcp->seq;