[ Upstream commit fb452a1aa3 ]
This reverts commit 6d7b857d54.
There is a bug in fragmentation codes use of the percpu_counter API,
that can cause issues on systems with many CPUs.
The frag_mem_limit() just reads the global counter (fbc->count),
without considering other CPUs can have upto batch size (130K) that
haven't been subtracted yet. Due to the 3MBytes lower thresh limit,
this become dangerous at >=24 CPUs (3*1024*1024/130000=24).
The correct API usage would be to use __percpu_counter_compare() which
does the right thing, and takes into account the number of (online)
CPUs and batch size, to account for this and call __percpu_counter_sum()
when needed.
We choose to revert the use of the lib/percpu_counter API for frag
memory accounting for several reasons:
1) On systems with CPUs > 24, the heavier fully locked
__percpu_counter_sum() is always invoked, which will be more
expensive than the atomic_t that is reverted to.
Given systems with more than 24 CPUs are becoming common this doesn't
seem like a good option. To mitigate this, the batch size could be
decreased and thresh be increased.
2) The add_frag_mem_limit+sub_frag_mem_limit pairs happen on the RX
CPU, before SKBs are pushed into sockets on remote CPUs. Given
NICs can only hash on L2 part of the IP-header, the NIC-RXq's will
likely be limited. Thus, a fair chance that atomic add+dec happen
on the same CPU.
Revert note that commit 1d6119baf0 ("net: fix percpu memory leaks")
removed init_frag_mem_limit() and instead use inet_frags_init_net().
After this revert, inet_frags_uninit_net() becomes empty.
Fixes: 6d7b857d54 ("net: use lib/percpu_counter API for fragmentation mem accounting")
Fixes: 1d6119baf0 ("net: fix percpu memory leaks")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
40bc5355e1