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rfs: annotate lockless accesses to RFS sock flow table

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[ Upstream commit 5c3b74a92aa285a3df722bf6329ba7ccf70346d6 ]

Add READ_ONCE()/WRITE_ONCE() on accesses to the sock flow table.

This also prevents a (smart ?) compiler to remove the condition in:

if (table->ents[index] != newval)
        table->ents[index] = newval;

We need the condition to avoid dirtying a shared cache line.

Fixes: fec5e652e5 ("rfs: Receive Flow Steering")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Eric Dumazet
2023-06-06 07:41:15 +00:00
committed by Greg Kroah-Hartman
parent c62ca9d037
commit dad7417db7
2 changed files with 9 additions and 4 deletions
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7
include/linux/netdevice.h
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@@ -744,8 +744,11 @@ static inline void rps_record_sock_flow(struct rps_sock_flow_table *table,
/* We only give a hint, preemption can change CPU under us */
val |= raw_smp_processor_id();
if (table->ents[index] != val)
table->ents[index] = val;
/* The following WRITE_ONCE() is paired with the READ_ONCE()
* here, and another one in get_rps_cpu().
*/
if (READ_ONCE(table->ents[index]) != val)
WRITE_ONCE(table->ents[index], val);
}
}