From 064c52b5c6036c916c0c142ba845da9abdf9f97e Mon Sep 17 00:00:00 2001
From: Nils Hoppmann <niho@linux.ibm.com>
Date: Mon, 9 Oct 2023 16:40:48 +0200
Subject: [PATCH] net/smc: Fix pos miscalculation in statistics
Git-commit: a950a5921db450c74212327f69950ff03419483a
Patch-mainline: v6.6-rc6
References: bsc#1218139
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 <pasic@linux.ibm.com>
Signed-off-by: Nils Hoppmann <niho@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
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 b60fe1eb37ab..a7bbc095894c 100644
--- a/net/smc/smc_stats.h
+++ b/net/smc/smc_stats.h
@@ -92,13 +92,14 @@ 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); \
} \
@@ -138,9 +139,12 @@ 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)
--
2.16.4