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authorAndi Kleen <ak@linux.intel.com>2009-12-23 21:00:20 +0100
committerAndi Kleen <ak@linux.intel.com>2009-12-23 21:00:20 +0100
commit4440095c8268c1a5e11577097d2be429cec036ca (patch)
tree7e1ca48bcd8fd0b947a7cc0edf31c0af9bbc4ec3 /kernel/sysctl_binary.c
parentf42ecb2808db5386f983d593a7c08d3ea3b94a27 (diff)
downloadlinux-2.6.34-ux500-4440095c8268c1a5e11577097d2be429cec036ca.tar.gz
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/sysctl_binary.c')
-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 112533d5fc0..8f5d16e0707 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)
return;
}
+#define WARN_ONCE_HASH_BITS 8
+#define WARN_ONCE_HASH_SIZE (1<<WARN_ONCE_HASH_BITS)
+
+static DECLARE_BITMAP(warn_once_bitmap, WARN_ONCE_HASH_SIZE);
+
+#define FNV32_OFFSET 2166136261U
+#define FNV32_PRIME 0x01000193
+
+/*
+ * Print each legacy sysctl (approximately) only once.
+ * To avoid making the tables non-const use a external
+ * hash-table instead.
+ * Worst case hash collision: 6, but very rarely.
+ * NOTE! We don't use the SMP-safe bit tests. We simply
+ * don't care enough.
+ */
+static void warn_on_bintable(const int *name, int nlen)
+{
+ int i;
+ u32 hash = FNV32_OFFSET;
+
+ for (i = 0; i < nlen; i++)
+ hash = (hash ^ name[i]) * FNV32_PRIME;
+ hash %= WARN_ONCE_HASH_SIZE;
+ if (__test_and_set_bit(hash, warn_once_bitmap))
+ return;
+ deprecated_sysctl_warning(name, nlen);
+}
+
static ssize_t do_sysctl(int __user *args_name, int nlen,
void __user *oldval, size_t oldlen, void __user *newval, size_t newlen)
{
@@ -1431,7 +1460,7 @@ static ssize_t do_sysctl(int __user *args_name, int nlen,
if (get_user(name[i], args_name + i))
return -EFAULT;
- deprecated_sysctl_warning(name, nlen);
+ warn_on_bintable(name, nlen);
return binary_sysctl(name, nlen, oldval, oldlen, newval, newlen);
}