• Steve Wise's avatar
    iw_cxgb4: refactor sq/rq drain logic · 4fe7c296
    Steve Wise authored
    With the addition of the IB/Core drain API, iw_cxgb4 supported drain
    by watching the CQs when the QP was out of RTS and signalling "drain
    complete" when the last CQE is polled.  This, however, doesn't fully
    support the drain semantics. Namely, the drain logic is supposed to signal
    "drain complete" only when the application has _processed_ the last CQE,
    not just removed them from the CQ.  Thus a small timing hole exists that
    can cause touch after free type bugs in applications using the drain API
    (nvmf, iSER, for example).  So iw_cxgb4 needs a better solution.
    
    The iWARP Verbs spec mandates that "_at some point_ after the QP is
    moved to ERROR", the iWARP driver MUST synchronously fail post_send and
    post_recv calls.  iw_cxgb4 was currently not allowing any posts once the
    QP is in ERROR.  This was in part due to the fact that the HW queues for
    the QP in ERROR state are disabled at this point, so there wasn't much
    else to do but fail the post operation synchronously.  This restriction
    is what drove the first drain implementation in iw_cxgb4 that has the
    above mentioned flaw.
    
    This patch changes iw_cxgb4 to allow post_send and post_recv WRs after
    the QP is moved to ERROR state for kernel mode users, thus still adhering
    to the Verbs spec for user mode users, but allowing flush WRs for kernel
    users.  Since the HW queues are disabled, we just synthesize a CQE for
    this post, queue it to the SW CQ, and then call the CQ event handler.
    This enables proper drain operations for the various storage applications.
    Signed-off-by: default avatarSteve Wise <swise@opengridcomputing.com>
    Signed-off-by: default avatarDoug Ledford <dledford@redhat.com>
    4fe7c296
t4.h 18.3 KB