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authorAndi Kleen <ak@linux.intel.com>2009-12-23 15:00:20 -0500
committerAndi Kleen <ak@linux.intel.com>2009-12-23 15:00:20 -0500
commit4440095c8268c1a5e11577097d2be429cec036ca (patch)
tree7e1ca48bcd8fd0b947a7cc0edf31c0af9bbc4ec3 /kernel
parentf42ecb2808db5386f983d593a7c08d3ea3b94a27 (diff)
SYSCTL: Print binary sysctl warnings (nearly) only once
When printing legacy sysctls print the warning message for each of them only once. This way there is a guarantee the syslog won't be flooded for any sane program. The original attempt at this made the tables non const and stored the flag inline. Linus suggested using a separate hash table for this, this is based on a code snippet from him. The hash implies this is not exact and can sometimes not print a new sysctl due to a hash collision, but in practice this should not be a problem I used a FNV32 hash over the binary string with a 32byte bitmap. This gives relatively little collisions when all the predefined binary sysctls are hashed: size 256 bucket length number 0: [25] 1: [67] 2: [88] 3: [47] 4: [22] 5: [6] 6: [1] The worst case is a single collision of 6 hash values. Signed-off-by: Andi Kleen <ak@linux.intel.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sysctl_binary.c31
1 files changed, 30 insertions, 1 deletions
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index 112533d5fc08..8f5d16e0707a 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -1417,6 +1417,35 @@ static void deprecated_sysctl_warning(const int *name, int nlen)
1417 return; 1417 return;
1418} 1418}
1419 1419
1420#define WARN_ONCE_HASH_BITS 8
1421#define WARN_ONCE_HASH_SIZE (1<<WARN_ONCE_HASH_BITS)
1422
1423static DECLARE_BITMAP(warn_once_bitmap, WARN_ONCE_HASH_SIZE);
1424
1425#define FNV32_OFFSET 2166136261U
1426#define FNV32_PRIME 0x01000193
1427
1428/*
1429 * Print each legacy sysctl (approximately) only once.
1430 * To avoid making the tables non-const use a external
1431 * hash-table instead.
1432 * Worst case hash collision: 6, but very rarely.
1433 * NOTE! We don't use the SMP-safe bit tests. We simply
1434 * don't care enough.
1435 */
1436static void warn_on_bintable(const int *name, int nlen)
1437{
1438 int i;
1439 u32 hash = FNV32_OFFSET;
1440
1441 for (i = 0; i < nlen; i++)
1442 hash = (hash ^ name[i]) * FNV32_PRIME;
1443 hash %= WARN_ONCE_HASH_SIZE;
1444 if (__test_and_set_bit(hash, warn_once_bitmap))
1445 return;
1446 deprecated_sysctl_warning(name, nlen);
1447}
1448
1420static ssize_t do_sysctl(int __user *args_name, int nlen, 1449static ssize_t do_sysctl(int __user *args_name, int nlen,
1421 void __user *oldval, size_t oldlen, void __user *newval, size_t newlen) 1450 void __user *oldval, size_t oldlen, void __user *newval, size_t newlen)
1422{ 1451{
@@ -1431,7 +1460,7 @@ static ssize_t do_sysctl(int __user *args_name, int nlen,
1431 if (get_user(name[i], args_name + i)) 1460 if (get_user(name[i], args_name + i))
1432 return -EFAULT; 1461 return -EFAULT;
1433 1462
1434 deprecated_sysctl_warning(name, nlen); 1463 warn_on_bintable(name, nlen);
1435 1464
1436 return binary_sysctl(name, nlen, oldval, oldlen, newval, newlen); 1465 return binary_sysctl(name, nlen, oldval, oldlen, newval, newlen);
1437} 1466}