Commit 4440095c8268c1a5e11577097d2be429cec036ca
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f42ecb2808
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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>
Showing 1 changed file with 30 additions and 1 deletions Side-by-side Diff
kernel/sysctl_binary.c
... | ... | @@ -1417,6 +1417,35 @@ |
1417 | 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 | + | |
1423 | +static 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 | + */ | |
1436 | +static 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 | + | |
1420 | 1449 | static ssize_t do_sysctl(int __user *args_name, int nlen, |
1421 | 1450 | void __user *oldval, size_t oldlen, void __user *newval, size_t newlen) |
1422 | 1451 | { |
... | ... | @@ -1431,7 +1460,7 @@ |
1431 | 1460 | if (get_user(name[i], args_name + i)) |
1432 | 1461 | return -EFAULT; |
1433 | 1462 | |
1434 | - deprecated_sysctl_warning(name, nlen); | |
1463 | + warn_on_bintable(name, nlen); | |
1435 | 1464 | |
1436 | 1465 | return binary_sysctl(name, nlen, oldval, oldlen, newval, newlen); |
1437 | 1466 | } |