From f05befe5c441b37ff1e033a01b6695a9a64d7d9c Mon Sep 17 00:00:00 2001 From: Nils Hoppmann Date: Mon, 9 Oct 2023 16:40:48 +0200 Subject: [PATCH] net/smc: Fix pos miscalculation in statistics [ Upstream commit a950a5921db450c74212327f69950ff03419483a ] SMC_STAT_PAYLOAD_SUB(_smc_stats, _tech, key, _len, _rc) will calculate wrong bucket positions for payloads of exactly 4096 bytes and (1 << (m + 12)) bytes, with m == SMC_BUF_MAX - 1. Intended bucket distribution: Assume l == size of payload, m == SMC_BUF_MAX - 1. Bucket 0 : 0 < l <= 2^13 Bucket n, 1 <= n <= m-1 : 2^(n+12) < l <= 2^(n+13) Bucket m : l > 2^(m+12) Current solution: _pos = fls64((l) >> 13) [...] _pos = (_pos < m) ? ((l == 1 << (_pos + 12)) ? _pos - 1 : _pos) : m For l == 4096, _pos == -1, but should be _pos == 0. For l == (1 << (m + 12)), _pos == m, but should be _pos == m - 1. In order to avoid special treatment of these corner cases, the calculation is adjusted. The new solution first subtracts the length by one, and then calculates the correct bucket by shifting accordingly, i.e. _pos = fls64((l - 1) >> 13), l > 0. This not only fixes the issues named above, but also makes the whole bucket assignment easier to follow. Same is done for SMC_STAT_RMB_SIZE_SUB(_smc_stats, _tech, k, _len), where the calculation of the bucket position is similar to the one named above. Fixes: e0e4b8fa5338 ("net/smc: Add SMC statistics support") Suggested-by: Halil Pasic Signed-off-by: Nils Hoppmann Reviewed-by: Halil Pasic Reviewed-by: Wenjia Zhang Reviewed-by: Dust Li Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- net/smc/smc_stats.h | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/net/smc/smc_stats.h b/net/smc/smc_stats.h index 4dbc237b7c19e..ee22d6f9a86aa 100644 --- a/net/smc/smc_stats.h +++ b/net/smc/smc_stats.h @@ -93,13 +93,14 @@ do { \ typeof(_smc_stats) stats = (_smc_stats); \ typeof(_tech) t = (_tech); \ typeof(_len) l = (_len); \ - int _pos = fls64((l) >> 13); \ + int _pos; \ typeof(_rc) r = (_rc); \ int m = SMC_BUF_MAX - 1; \ this_cpu_inc((*stats).smc[t].key ## _cnt); \ - if (r <= 0) \ + if (r <= 0 || l <= 0) \ break; \ - _pos = (_pos < m) ? ((l == 1 << (_pos + 12)) ? _pos - 1 : _pos) : m; \ + _pos = fls64((l - 1) >> 13); \ + _pos = (_pos <= m) ? _pos : m; \ this_cpu_inc((*stats).smc[t].key ## _pd.buf[_pos]); \ this_cpu_add((*stats).smc[t].key ## _bytes, r); \ } \ @@ -139,9 +140,12 @@ while (0) do { \ typeof(_len) _l = (_len); \ typeof(_tech) t = (_tech); \ - int _pos = fls((_l) >> 13); \ + int _pos; \ int m = SMC_BUF_MAX - 1; \ - _pos = (_pos < m) ? ((_l == 1 << (_pos + 12)) ? _pos - 1 : _pos) : m; \ + if (_l <= 0) \ + break; \ + _pos = fls((_l - 1) >> 13); \ + _pos = (_pos <= m) ? _pos : m; \ this_cpu_inc((*(_smc_stats)).smc[t].k ## _rmbsize.buf[_pos]); \ } \ while (0) -- 2.39.5