On Tue, Sep 09, 2025 at 06:00:36PM +0200, Philipp Reisner wrote: > On Tue, Sep 9, 2025 at 5:31 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > > > On Tue, Sep 09, 2025 at 04:48:19PM +0200, Philipp Reisner wrote: > > > On Mon, Sep 8, 2025 at 4:25 PM Leon Romanovsky <leon@xxxxxxxxxx> wrote: > > > > > > > > On Fri, Aug 22, 2025 at 10:19:41AM +0200, Philipp Reisner wrote: > > > > > Allow the comp_handler callback implementation to call ib_poll_cq(). > > > > > A call to ib_poll_cq() calls rxe_poll_cq() with the rdma_rxe driver. > > > > > And rxe_poll_cq() locks cq->cq_lock. That leads to a spinlock deadlock. > > > > > > > > Can you please be more specific about the deadlock? > > > > Please write call stack to describe it. > > > > > > > Instead of a call stack, I write it from top to bottom: > > > > > > The line numbers in the .c files are valid for Linux-6.16: > > > > > > 1 rxe_cq_post() [rxe_cq.c:85] > > > 2 spin_lock_irqsave() [rxe_cq.c:93] > > > 3 cq->ibcq.comp_handler() [rxe_cq.c:116] > > > 4 some_comp_handler() > > > 5 ib_poll_cq() > > > 6 cq->device->ops.poll_cq() [ib_verbs.h:4037] > > > 7 rxe_poll_cq() [rxe_verbs.c:1165] > > > 8 spin_lock_irqsave() [rxe_verbs.c:1172] > > > > > > In line 8 of this call graph, it deadlocks because the spinlock > > > was already acquired in line 2 of the call graph. > > > > Is this even legal in verbs? I'm not sure you can do pull cq from a > > interrupt driven comp handler.. Is something already doing this intree? > > > > The file drivers/infiniband/sw/rdmavt/cq.c has this comment: > /* > * The completion handler will most likely rearm the notification > * and poll for all pending entries. If a new completion entry > * is added while we are in this routine, queue_work() > * won't call us again until we return so we check triggered to > * see if we need to call the handler again. > */ > > Also, Intel and Mellanox cards and drivers allow calling ib_poll_cq() > from the completion handler. And do these drivers drop CQ lock like you are proposing here? > > The problem exists only with the RXE driver.
