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yield() in netlink_broadcast_filtered

DISCUSSION Fredrick 2 participants 2 messages Apr 6, 2012

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Fredrick

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#0 lore raw

I see there is a yield being called from netlink_broadcast_filtered.
.....
int netlink_broadcast_filtered(...)
{
....

        if (info.delivered) {
                if (info.congested && (allocation & __GFP_WAIT))
                        yield();
                return 0;
        }
        return -ESRCH;
}

.....

But I don't see the point of calling it. After the yield, there is nothing being done. It just returns. So why yield ?
Why can't it simply return?

-Fredrick

#1 lore raw
Quoted 15 lines · On Fri, 06 Apr 2012 07:11:56 -0700 Fredrick <[email protected]> wrote:

I see there is a yield being called from netlink_broadcast_filtered.
.....
int netlink_broadcast_filtered(...)
{
....

         if (info.delivered) {
                 if (info.congested && (allocation & __GFP_WAIT))
                         yield();
                 return 0;
         }
         return -ESRCH;
}
Quoted 7 lines

.....

But I don't see the point of calling it. After the yield, there is nothing being done. It just returns. So why yield ?
Why can't it simply return?

Because without that yield it is easily possible for one process to generate lots of netlink messages and overrun the consumers. The yield allows the now ready listening processes to run. There is no good mechanism to totally prevent overrunning the socket of processes reading for netlink events, but this yield() is good enough to avoid the problem with the typical case. The example we are familar with is a full route table (1M routes) and a link change causing a routing flap.