diff options
Diffstat (limited to 'ipc/util.c')
| -rw-r--r-- | ipc/util.c | 35 |
1 files changed, 30 insertions, 5 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; } |