Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH v5 5/9] IB/isert: Replace semaphore sem with completion | Date | Mon, 21 Nov 2016 15:50:59 +0100 |
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On Monday, November 21, 2016 2:33:02 PM CET Sagi Grimberg wrote: > >>> diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c > >>> index 6dd43f6..de80f56 100644 > >>> --- a/drivers/infiniband/ulp/isert/ib_isert.c > >>> +++ b/drivers/infiniband/ulp/isert/ib_isert.c > >>> @@ -619,7 +619,7 @@ > >>> mutex_unlock(&isert_np->mutex); > >>> > >>> isert_info("np %p: Allow accept_np to continue\n", isert_np); > >>> - up(&isert_np->sem); > >>> + complete(&isert_np->comp); > >>> } > >>> > >>> static void > >>> @@ -2311,7 +2311,7 @@ struct rdma_cm_id * > >>> isert_err("Unable to allocate struct isert_np\n"); > >>> return -ENOMEM; > >>> } > >>> - sema_init(&isert_np->sem, 0); > >>> + init_completion(&isert_np->comp); > >> > >> This is still racy, a connect event can complete just before we > >> init the completion and *will* get lost... > >> > >> This code started off with a waitqueue which exposes the same > >> problem, see: > >> 531b7bf4bd79 Target/iser: Fix iscsit_accept_np and rdma_cm racy flow > >> > >> So, still NAK from me... > > > > I don't see what you mean here. The code using a waitqueue had no > > counter but the completion does. > > The problem here is that init_completion sets the counter to zero > and between this thread wakes up and until it initializes comp->done > we might have another connect event completing it and I fail to > see how this is handled correctly.
But the sema_init()/init_completion() is done right after the structure is allocated, so nothing should have a pointer to it at this time.
Later when we do the down()/wait_for_completion(), that will just decrement the counter rather than initialize, and converting from one to the other doesn't change anything here.
Arnd
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