On Mon, Jul 9, 2018 at 5:10 PM, Manfred Spraul <manf...@colorfullife.com> wrote:
> If idr_alloc within ipc_idr_alloc fails, then the return value (-ENOSPC)
> is used to calculate new->id.
> Technically, this is not a bug, because new->id is never accessed.
>
> But: Clean it up anyways: On error, just return, do not set new->id.
> And improve the documentation.
>
> Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
> Cc: Dmitry Vyukov <dvyu...@google.com>
> ---
> ipc/util.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/ipc/util.c b/ipc/util.c
> index d474f2b3b299..302c18fc846b 100644
> --- a/ipc/util.c
> +++ b/ipc/util.c
> @@ -182,11 +182,20 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids
> *ids, key_t key)
> }
>
> /*
> - * Specify desired id for next allocated IPC object.
> + * Insert new IPC object into idr tree, and set sequence number and id
> + * in the correct order.
> + * Especially:
> + * - the sequence number must be set before inserting the object into the
> idr,
> + * because the sequence number is accessed without a lock.
> + * - the id can/must be set after inserting the object into the idr.
> + * All accesses must be done after getting kern_ipc_perm.lock.
> + *
> + * The caller must own kern_ipc_perm.lock.of the new object.
> + * On error, the function returns a (negative) error code.
> */
> static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm
> *new)
> {
> - int key, next_id = -1;
> + int id, next_id = -1;
/\/\/\/\
Looks good to me. I was also confused by how key transforms into id,
and then key name is used for something else.
> #ifdef CONFIG_CHECKPOINT_RESTORE
> next_id = ids->next_id;
> @@ -197,14 +206,15 @@ static inline int ipc_idr_alloc(struct ipc_ids *ids,
> struct kern_ipc_perm *new)
> new->seq = ids->seq++;
> if (ids->seq > IPCID_SEQ_MAX)
> ids->seq = 0;
> - key = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT);
> + id = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT);
> } else {
> new->seq = ipcid_to_seqx(next_id);
> - key = idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id),
> + id = idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id),
> 0, GFP_NOWAIT);
> }
> - new->id = SEQ_MULTIPLIER * new->seq + key;
> - return key;
> + if (id >= 0)
> + new->id = SEQ_MULTIPLIER * new->seq + id;
We still initialize seq in this case. I guess it's ok because the
object is not published at all. But if we are doing this, then perhaps
store seq into a local var first and then:
if (id >= 0) {
new->id = SEQ_MULTIPLIER * seq + id;
new->seq = seq:
}
?
But I don't have a strong preference, so if it's the only reason to
resend series then perhaps it's not worth it.
Thanks
> + return id;
> }
>
> /**
> --
> 2.17.1
>
