Revision 3770a42bb8ceb856877699257a43c0585a5d2996 authored by Sagi Grimberg on 05 September 2022, 15:07:06 UTC, committed by Christoph Hellwig on 06 September 2022, 04:40:44 UTC
When we queue requests, we strive to batch as much as possible and also signal the network stack that more data is about to be sent over a socket with MSG_SENDPAGE_NOTLAST. This flag looks at the pending requests queued as well as queue->more_requests that is derived from the block layer last-in-batch indication. We set more_request=true when we flush the request directly from .queue_rq submission context (in nvme_tcp_send_all), however this is wrongly assuming that no other requests may be queued during the execution of nvme_tcp_send_all. Due to this, a race condition may happen where: 1. request X is queued as !last-in-batch 2. request X submission context calls nvme_tcp_send_all directly 3. nvme_tcp_send_all is preempted and schedules to a different cpu 4. request Y is queued as last-in-batch 5. nvme_tcp_send_all context sends request X+Y, however signals for both MSG_SENDPAGE_NOTLAST because queue->more_requests=true. ==> none of the requests is pushed down to the wire as the network stack is waiting for more data, both requests timeout. To fix this, we eliminate queue->more_requests and only rely on the queue req_list and send_list to be not-empty. Fixes: 122e5b9f3d37 ("nvme-tcp: optimize network stack with setting msg flags according to batch size") Reported-by: Jonathan Nicklin <jnicklin@blockbridge.com> Signed-off-by: Sagi Grimberg <sagi@grimberg.me> Tested-by: Jonathan Nicklin <jnicklin@blockbridge.com> Signed-off-by: Christoph Hellwig <hch@lst.de>
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