[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCHv3 net] xen-netback: fix race between napi_complete() and interrupt handler
On 16/05/14 12:21, Wei Liu wrote: > On Fri, May 16, 2014 at 12:20:02PM +0100, David Vrabel wrote: >> When the NAPI budget was not all used, xenvif_poll() would call >> napi_complete() /after/ enabling the interrupt. This resulted in a >> race between the napi_complete() and the napi_schedule() in the >> interrupt handler. The use of local_irq_save/restore() avoided by >> race iff the handler is running on the same CPU but not if it was >> running on a different CPU. >> >> Fix this properly by calling napi_complete() before reenabling >> interrupts (in the xenvif_napi_schedule_or_enable_irq() call). >> >> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx> >> Acked-by: Wei Lui <wei.lui2@xxxxxxxxxx> > > It's "Liu". ;-) Sorry! Dave, can you take this instead: 8<-------------- xen-netback: fix race between napi_complete() and interrupt handler When the NAPI budget was not all used, xenvif_poll() would call napi_complete() /after/ enabling the interrupt. This resulted in a race between the napi_complete() and the napi_schedule() in the interrupt handler. The use of local_irq_save/restore() avoided by race iff the handler is running on the same CPU but not if it was running on a different CPU. Fix this properly by calling napi_complete() before reenabling interrupts (in the xenvif_napi_schedule_or_enable_irq() call). Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx> Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx> --- v3: - new name is xenvif_napi_schedule_or_enable_events(). v2: - Rename xenvif_check_rx_xenvif() to xenvif_napi_schedule_or_enable_irq() to make it more obvious what it does. --- drivers/net/xen-netback/common.h | 2 +- drivers/net/xen-netback/interface.c | 30 +++--------------------------- drivers/net/xen-netback/netback.c | 4 ++-- 3 files changed, 6 insertions(+), 30 deletions(-) diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h index ae413a2..d66de9a 100644 --- a/drivers/net/xen-netback/common.h +++ b/drivers/net/xen-netback/common.h @@ -209,7 +209,7 @@ int xenvif_map_frontend_rings(struct xenvif *vif, grant_ref_t rx_ring_ref); /* Check for SKBs from frontend and schedule backend processing */ -void xenvif_check_rx_xenvif(struct xenvif *vif); +void xenvif_napi_schedule_or_enable_events(struct xenvif *vif); /* Prevent the device from generating any further traffic. */ void xenvif_carrier_off(struct xenvif *vif); diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c index 7669d49..0200de2 100644 --- a/drivers/net/xen-netback/interface.c +++ b/drivers/net/xen-netback/interface.c @@ -65,32 +65,8 @@ static int xenvif_poll(struct napi_struct *napi, int budget) work_done = xenvif_tx_action(vif, budget); if (work_done < budget) { - int more_to_do = 0; - unsigned long flags; - - /* It is necessary to disable IRQ before calling - * RING_HAS_UNCONSUMED_REQUESTS. Otherwise we might - * lose event from the frontend. - * - * Consider: - * RING_HAS_UNCONSUMED_REQUESTS - * <frontend generates event to trigger napi_schedule> - * __napi_complete - * - * This handler is still in scheduled state so the - * event has no effect at all. After __napi_complete - * this handler is descheduled and cannot get - * scheduled again. We lose event in this case and the ring - * will be completely stalled. - */ - - local_irq_save(flags); - - RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do); - if (!more_to_do) - __napi_complete(napi); - - local_irq_restore(flags); + napi_complete(napi); + xenvif_napi_schedule_or_enable_events(vif); } return work_done; @@ -166,7 +142,7 @@ static void xenvif_up(struct xenvif *vif) enable_irq(vif->tx_irq); if (vif->tx_irq != vif->rx_irq) enable_irq(vif->rx_irq); - xenvif_check_rx_xenvif(vif); + xenvif_napi_schedule_or_enable_events(vif); } static void xenvif_down(struct xenvif *vif) diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c index e5284bc..0efda31 100644 --- a/drivers/net/xen-netback/netback.c +++ b/drivers/net/xen-netback/netback.c @@ -604,7 +604,7 @@ done: notify_remote_via_irq(vif->rx_irq); } -void xenvif_check_rx_xenvif(struct xenvif *vif) +void xenvif_napi_schedule_or_enable_events(struct xenvif *vif) { int more_to_do; @@ -638,7 +638,7 @@ static void tx_credit_callback(unsigned long data) { struct xenvif *vif = (struct xenvif *)data; tx_add_credit(vif); - xenvif_check_rx_xenvif(vif); + xenvif_napi_schedule_or_enable_events(vif); } static void xenvif_tx_err(struct xenvif *vif, -- 1.7.10.4 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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