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| author | Jesper Dangaard Brouer <brouer@redhat.com> | 2017-09-01 11:26:08 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-09-03 20:01:05 +0200 |
| commit | fb452a1aa3fd4034d7999e309c5466ff2d7005aa (patch) | |
| tree | 929f2e7692f05a685de60535e2de27aa37579400 /net/ipv4 | |
| parent | ipv4: Don't override return code from ip_route_input_noref() (diff) | |
| download | linux-fb452a1aa3fd4034d7999e309c5466ff2d7005aa.tar.xz linux-fb452a1aa3fd4034d7999e309c5466ff2d7005aa.zip | |
Revert "net: use lib/percpu_counter API for fragmentation mem accounting"
This reverts commit 6d7b857d541ecd1d9bd997c97242d4ef94b19de2.
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 1d6119baf061 ("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: 6d7b857d541e ("net: use lib/percpu_counter API for fragmentation mem accounting")
Fixes: 1d6119baf061 ("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>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/inet_fragment.c | 4 |
1 files changed, 1 insertions, 3 deletions
diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c index 96e95e83cc61..af74d0433453 100644 --- a/net/ipv4/inet_fragment.c +++ b/net/ipv4/inet_fragment.c @@ -234,10 +234,8 @@ evict_again: cond_resched(); if (read_seqretry(&f->rnd_seqlock, seq) || - percpu_counter_sum(&nf->mem)) + sum_frag_mem_limit(nf)) goto evict_again; - - percpu_counter_destroy(&nf->mem); } EXPORT_SYMBOL(inet_frags_exit_net); |