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-rw-r--r--ipc/util.c35
-rw-r--r--ipc/util.h8
2 files changed, 34 insertions, 9 deletions
diff --git a/ipc/util.c b/ipc/util.c
index cf5d1087409e..71f3f3982fc8 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -119,6 +119,7 @@ void ipc_init_ids(struct ipc_ids *ids)
rhashtable_init(&ids->key_ht, &ipc_kht_params);
idr_init(&ids->ipcs_idr);
ids->max_idx = -1;
+ ids->last_idx = -1;
#ifdef CONFIG_CHECKPOINT_RESTORE
ids->next_id = -1;
#endif
@@ -192,6 +193,10 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
*
* The caller must own kern_ipc_perm.lock.of the new object.
* On error, the function returns a (negative) error code.
+ *
+ * To conserve sequence number space, especially with extended ipc_mni,
+ * the sequence number is incremented only when the returned ID is less than
+ * the last one.
*/
static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new)
{
@@ -215,17 +220,37 @@ static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new)
*/
if (next_id < 0) { /* !CHECKPOINT_RESTORE or next_id is unset */
- new->seq = ids->seq++;
- if (ids->seq > IPCID_SEQ_MAX)
- ids->seq = 0;
- idx = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT);
+
+ /* allocate the idx, with a NULL struct kern_ipc_perm */
+ idx = idr_alloc(&ids->ipcs_idr, NULL, 0, 0, GFP_NOWAIT);
+
+ if (idx >= 0) {
+ /*
+ * idx got allocated successfully.
+ * Now calculate the sequence number and set the
+ * pointer for real.
+ */
+ if (idx <= ids->last_idx) {
+ ids->seq++;
+ if (ids->seq >= ipcid_seq_max())
+ ids->seq = 0;
+ }
+ ids->last_idx = idx;
+
+ new->seq = ids->seq;
+ /* no need for smp_wmb(), this is done
+ * inside idr_replace, as part of
+ * rcu_assign_pointer
+ */
+ idr_replace(&ids->ipcs_idr, new, idx);
+ }
} else {
new->seq = ipcid_to_seqx(next_id);
idx = idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id),
0, GFP_NOWAIT);
}
if (idx >= 0)
- new->id = (new->seq << IPCMNI_SEQ_SHIFT) + idx;
+ new->id = (new->seq << ipcmni_seq_shift()) + idx;
return idx;
}
diff --git a/ipc/util.h b/ipc/util.h
index 9746886757de..8c834ed39012 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -34,13 +34,13 @@
extern int ipc_mni;
extern int ipc_mni_shift;
-#define IPCMNI_SEQ_SHIFT ipc_mni_shift
+#define ipcmni_seq_shift() ipc_mni_shift
#define IPCMNI_IDX_MASK ((1 << ipc_mni_shift) - 1)
#else /* CONFIG_SYSVIPC_SYSCTL */
#define ipc_mni IPCMNI
-#define IPCMNI_SEQ_SHIFT IPCMNI_SHIFT
+#define ipcmni_seq_shift() IPCMNI_SHIFT
#define IPCMNI_IDX_MASK ((1 << IPCMNI_SHIFT) - 1)
#endif /* CONFIG_SYSVIPC_SYSCTL */
@@ -123,8 +123,8 @@ struct pid_namespace *ipc_seq_pid_ns(struct seq_file *);
#define IPC_SHM_IDS 2
#define ipcid_to_idx(id) ((id) & IPCMNI_IDX_MASK)
-#define ipcid_to_seqx(id) ((id) >> IPCMNI_SEQ_SHIFT)
-#define IPCID_SEQ_MAX (INT_MAX >> IPCMNI_SEQ_SHIFT)
+#define ipcid_to_seqx(id) ((id) >> ipcmni_seq_shift())
+#define ipcid_seq_max() (INT_MAX >> ipcmni_seq_shift())
/* must be called with ids->rwsem acquired for writing */
int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int);