Quoting r. Zach Brown <[email protected]>:
> Subject: [PATCH] mthca: initialize send and receive queue locks separately
>
> mthca: initialize send and receive queue locks separately
>
> lockdep identifies a lock by the call site of its initialization. By
> initializing the send and receive queue locks in mthca_wq_init() we confuse
> lockdep. It warns that that the ordered acquiry of both locks in
> mthca_modify_qp() is recursive acquiry of one lock:
>
> =============================================
> [ INFO: possible recursive locking detected ]
> ---------------------------------------------
> modprobe/1192 is trying to acquire lock:
> (&wq->lock){....}, at: [<f892b4db>] mthca_modify_qp+0x60/0xa7b [ib_mthca]
> but task is already holding lock:
> (&wq->lock){....}, at: [<f892b4ce>] mthca_modify_qp+0x53/0xa7b [ib_mthca]
Is this mthca code unique?
Would not it be better to teach lockdep about this scenario somehow?
> Initializing the locks separately in mthca_alloc_qp_common() stops the warning
> and will let lockdep enforce proper ordering on paths that acquire both locks.
>
> Signed-off-by: Zach Brown <[email protected]>
This moves code out of a common function and so results in code duplication
and has memory cost.
> ---
>
> drivers/infiniband/hw/mthca/mthca_qp.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
> Index: 2.6.17-mm6/drivers/infiniband/hw/mthca/mthca_qp.c
> ===================================================================
> --- 2.6.17-mm6.orig/drivers/infiniband/hw/mthca/mthca_qp.c 2006-07-03 08:41:16.000000000 -0400
> +++ 2.6.17-mm6/drivers/infiniband/hw/mthca/mthca_qp.c 2006-07-03 10:05:52.000000000 -0400
> @@ -224,7 +224,7 @@
>
> static void mthca_wq_init(struct mthca_wq *wq)
> {
> - spin_lock_init(&wq->lock);
> + /* mthca_alloc_qp_common() initializes the locks */
> wq->next_ind = 0;
> wq->last_comp = wq->max - 1;
> wq->head = 0;
And then we'll have to remember to update this comment when lock
is moved to another place?
> @@ -1114,6 +1114,9 @@
> qp->sq_policy = send_policy;
> mthca_wq_init(&qp->sq);
> mthca_wq_init(&qp->rq);
> + /* these are initialized separately so lockdep can tell them apart */
> + spin_lock_init(&qp->sq.lock);
> + spin_lock_init(&qp->rq.lock);
>
> ret = mthca_map_memfree(dev, qp);
> if (ret)
>
Looks wrong, to me. Is it a good idea to fix correct code?
Assuming its important, can we maybe add some annotations to make lockdep shut
up, instead?
--
MST
-
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