linux/net/core/utils.c, branch v3.16

net: avoid dependency of net_get_random_once on nop patching

2014-05-14T04:37:34Z

net_get_random_once depends on the static keys infrastructure to patch up the branch to the slow path during boot. This was realized by abusing the static keys api and defining a new initializer to not enable the call site while still indicating that the branch point should get patched up. This was needed to have the fast path considered likely by gcc. The static key initialization during boot up normally walks through all the registered keys and either patches in ideal nops or enables the jump site but omitted that step on x86 if ideal nops where already placed at static_key branch points. Thus net_get_random_once branches not always became active. This patch switches net_get_random_once to the ordinary static_key api and thus places the kernel fast path in the - by gcc considered - unlikely path. Microbenchmarks on Intel and AMD x86-64 showed that the unlikely path actually beats the likely path in terms of cycle cost and that different nop patterns did not make much difference, thus this switch should not be noticeable. Fixes: a48e42920ff38b ("net: introduce new macro net_get_random_once") Reported-by: Tuomas Räsänen Cc: Linus Torvalds Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller

net: make net_get_random_once irq safe

2013-10-25T23:03:39Z

I initial build non irq safe version of net_get_random_once because I would liked to have the freedom to defer even the extraction process of get_random_bytes until the nonblocking pool is fully seeded. I don't think this is a good idea anymore and thus this patch makes net_get_random_once irq safe. Now someone using net_get_random_once does not need to care from where it is called. Cc: David S. Miller Cc: Eric Dumazet Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller

net: introduce new macro net_get_random_once

2013-10-19T23:45:35Z

net_get_random_once is a new macro which handles the initialization of secret keys. It is possible to call it in the fast path. Only the initialization depends on the spinlock and is rather slow. Otherwise it should get used just before the key is used to delay the entropy extration as late as possible to get better randomness. It returns true if the key got initialized. The usage of static_keys for net_get_random_once is a bit uncommon so it needs some further explanation why this actually works: === In the simple non-HAVE_JUMP_LABEL case we actually have === no constrains to use static_key_(true|false) on keys initialized with STATIC_KEY_INIT_(FALSE|TRUE). So this path just expands in favor of the likely case that the initialization is already done. The key is initialized like this: ___done_key = { .enabled = ATOMIC_INIT(0) } The check if (!static_key_true(&___done_key)) \ expands into (pseudo code) if (!likely(___done_key > 0)) , so we take the fast path as soon as ___done_key is increased from the helper function. === If HAVE_JUMP_LABELs are available this depends === on patching of jumps into the prepared NOPs, which is done in jump_label_init at boot-up time (from start_kernel). It is forbidden and dangerous to use net_get_random_once in functions which are called before that! At compilation time NOPs are generated at the call sites of net_get_random_once. E.g. net/ipv6/inet6_hashtable.c:inet6_ehashfn (we need to call net_get_random_once two times in inet6_ehashfn, so two NOPs): 71: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) 76: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) Both will be patched to the actual jumps to the end of the function to call __net_get_random_once at boot time as explained above. arch_static_branch is optimized and inlined for false as return value and actually also returns false in case the NOP is placed in the instruction stream. So in the fast case we get a "return false". But because we initialize ___done_key with (enabled != (entries & 1)) this call-site will get patched up at boot thus returning true. The final check looks like this: if (!static_key_true(&___done_key)) \ ___ret = __net_get_random_once(buf, \ expands to if (!!static_key_false(&___done_key)) \ ___ret = __net_get_random_once(buf, \ So we get true at boot time and as soon as static_key_slow_inc is called on the key it will invert the logic and return false for the fast path. static_key_slow_inc will change the branch because it got initialized with .enabled == 0. After static_key_slow_inc is called on the key the branch is replaced with a nop again. === Misc: === The helper defers the increment into a workqueue so we don't have problems calling this code from atomic sections. A seperate boolean (___done) guards the case where we enter net_get_random_once again before the increment happend. Cc: Ingo Molnar Cc: Steven Rostedt Cc: Jason Baron Cc: Peter Zijlstra Cc: Eric Dumazet Cc: "David S. Miller" Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller

net: core: move mac_pton() to lib/net_utils.c

2013-06-05T19:00:27Z

Since we have at least one user of this function outside of CONFIG_NET scope, we have to provide this function independently. The proposed solution is to move it under lib/net_utils.c with corresponding configuration variable and select wherever it is needed. Signed-off-by: Andy Shevchenko Reported-by: Arnd Bergmann Acked-by: David S. Miller Acked-by: Arnd Bergmann Signed-off-by: Greg Kroah-Hartman

net: core: let's use native isxdigit instead of custom

2013-03-27T16:48:32Z

In kernel we have fast and pretty implementation of the isxdigit() function. Let's use it. Signed-off-by: Andy Shevchenko Signed-off-by: David S. Miller

net: add doc for in4_pton()

2012-10-12T17:56:52Z

It is not easy to use in4_pton() correctly without reading its definition, so add some doc for it. Cc: David S. Miller Signed-off-by: Cong Wang Signed-off-by: David S. Miller

net: add doc for in6_pton()

2012-10-12T17:56:52Z

It is not easy to use in6_pton() correctly without reading its definition, so add some doc for it. Cc: David S. Miller Signed-off-by: Cong Wang Signed-off-by: David S. Miller

net: core: add function for incremental IPv6 pseudo header checksum updates

2012-08-30T01:00:16Z

Add inet_proto_csum_replace16 for incrementally updating IPv6 pseudo header checksums for IPv6 NAT. Signed-off-by: Patrick McHardy Acked-by: David S. Miller

net: Fixed coding style issues relating to braces.

2012-04-12T20:35:48Z

Fixed coding style issues in net/core/utils.c in relation with braces placement. Signed-off-by: Jeffrin Jose Signed-off-by: David S. Miller

Remove all #inclusions of asm/system.h

2012-03-28T17:30:03Z

Remove all #inclusions of asm/system.h preparatory to splitting and killing it. Performed with the following command: perl -p -i -e 's!^#\s*include\s*.*\n!!' `grep -Irl '^#\s*include\s*' *` Signed-off-by: David Howells