diff options
| -rw-r--r-- | include/linux/ipc_namespace.h | 1 | ||||
| -rw-r--r-- | ipc/util.c | 35 | ||||
| -rw-r--r-- | ipc/util.h | 8 |
3 files changed, 35 insertions, 9 deletions
diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h index 6ab8c1bada3f..c309f43bde45 100644 --- a/include/linux/ipc_namespace.h +++ b/include/linux/ipc_namespace.h @@ -19,6 +19,7 @@ struct ipc_ids { struct rw_semaphore rwsem; struct idr ipcs_idr; int max_idx; + int last_idx; /* For wrap around detection */ #ifdef CONFIG_CHECKPOINT_RESTORE int next_id; #endif 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); |