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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@citrix.com> Acked-by: Wei Liu <wei.liu2@citrix.com> Acked-by: Ian Campbell <ian.campbell@citrix.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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parent
202630b445
commit
0d08fceb2e
3 changed files with 6 additions and 30 deletions
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@ -226,7 +226,7 @@ int xenvif_map_frontend_rings(struct xenvif *vif,
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grant_ref_t rx_ring_ref);
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/* Check for SKBs from frontend and schedule backend processing */
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void xenvif_check_rx_xenvif(struct xenvif *vif);
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void xenvif_napi_schedule_or_enable_events(struct xenvif *vif);
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/* Prevent the device from generating any further traffic. */
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void xenvif_carrier_off(struct xenvif *vif);
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@ -75,32 +75,8 @@ static int xenvif_poll(struct napi_struct *napi, int budget)
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work_done = xenvif_tx_action(vif, budget);
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if (work_done < budget) {
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int more_to_do = 0;
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unsigned long flags;
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/* It is necessary to disable IRQ before calling
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* RING_HAS_UNCONSUMED_REQUESTS. Otherwise we might
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* lose event from the frontend.
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*
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* Consider:
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* RING_HAS_UNCONSUMED_REQUESTS
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* <frontend generates event to trigger napi_schedule>
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* __napi_complete
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*
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* This handler is still in scheduled state so the
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* event has no effect at all. After __napi_complete
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* this handler is descheduled and cannot get
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* scheduled again. We lose event in this case and the ring
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* will be completely stalled.
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*/
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local_irq_save(flags);
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RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);
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if (!more_to_do)
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__napi_complete(napi);
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local_irq_restore(flags);
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napi_complete(napi);
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xenvif_napi_schedule_or_enable_events(vif);
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}
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return work_done;
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@ -194,7 +170,7 @@ static void xenvif_up(struct xenvif *vif)
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enable_irq(vif->tx_irq);
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if (vif->tx_irq != vif->rx_irq)
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enable_irq(vif->rx_irq);
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xenvif_check_rx_xenvif(vif);
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xenvif_napi_schedule_or_enable_events(vif);
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}
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static void xenvif_down(struct xenvif *vif)
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@ -716,7 +716,7 @@ static void xenvif_rx_action(struct xenvif *vif)
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notify_remote_via_irq(vif->rx_irq);
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}
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void xenvif_check_rx_xenvif(struct xenvif *vif)
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void xenvif_napi_schedule_or_enable_events(struct xenvif *vif)
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{
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int more_to_do;
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@ -750,7 +750,7 @@ static void tx_credit_callback(unsigned long data)
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{
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struct xenvif *vif = (struct xenvif *)data;
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tx_add_credit(vif);
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xenvif_check_rx_xenvif(vif);
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xenvif_napi_schedule_or_enable_events(vif);
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}
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static void xenvif_tx_err(struct xenvif *vif,
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