This is a note to let you know that I've just added the patch titled
net/smc: Fix pos miscalculation in statistics
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-smc-fix-pos-miscalculation-in-statistics.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ca0ff90b0a3a5ea53a8244f5cca42d5c5cdfbff0
Author: Nils Hoppmann <niho@xxxxxxxxxxxxx>
Date: Mon Oct 9 16:40:48 2023 +0200
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 <pasic@xxxxxxxxxxxxx>
Signed-off-by: Nils Hoppmann <niho@xxxxxxxxxxxxx>
Reviewed-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
Reviewed-by: Wenjia Zhang <wenjia@xxxxxxxxxxxxx>
Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/smc/smc_stats.h b/net/smc/smc_stats.h
index aa8928975cc63..9d32058db2b5d 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)
