Hello Stephen Hemminger,
The patch 15e1674de747: "vmbus: add prefetch to ring buffer iterator"
from Jun 25, 2017, leads to the following static checker warning:
drivers/hv/ring_buffer.c:366 hv_pkt_iter_first()
warn: 'desc' can't be NULL.
drivers/hv/ring_buffer.c
357 struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
358 {
359 struct hv_ring_buffer_info *rbi = &channel->inbound;
360 struct vmpacket_descriptor *desc;
361
362 if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
363 return NULL;
364
365 desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
366 if (desc)
367 prefetch((char *)desc + (desc->len8 << 3));
368
369 return desc;
370 }
371 EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
This static checker warning is pretty bogus, but it's actually correct
this time (like a stopped clock is right twice a day). The first test
ensures that there is enough space in the ring bugger so it can't return
NULL.
How does that ring buffer work without any sort of locking?? It feels
like you should have to say how much data you want to get in
hv_get_ring_buffer() so that someone else doesn't come and claim it
between the check for if it's avaible and the get.
regards,
dan carpenter
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