diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/atomic_ops.txt | 4 | ||||
| -rw-r--r-- | Documentation/fault-injection/fault-injection.txt | 11 | ||||
| -rw-r--r-- | Documentation/memory-barriers.txt | 6 | ||||
| -rw-r--r-- | Documentation/static-keys.txt | 99 |
4 files changed, 69 insertions, 51 deletions
diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt index dab6da3382d9..b19fc34efdb1 100644 --- a/Documentation/atomic_ops.txt +++ b/Documentation/atomic_ops.txt @@ -266,7 +266,9 @@ with the given old and new values. Like all atomic_xxx operations, atomic_cmpxchg will only satisfy its atomicity semantics as long as all other accesses of *v are performed through atomic_xxx operations. -atomic_cmpxchg must provide explicit memory barriers around the operation. +atomic_cmpxchg must provide explicit memory barriers around the operation, +although if the comparison fails then no memory ordering guarantees are +required. The semantics for atomic_cmpxchg are the same as those defined for 'cas' below. diff --git a/Documentation/fault-injection/fault-injection.txt b/Documentation/fault-injection/fault-injection.txt index 4cf1a2a6bd72..415484f3d59a 100644 --- a/Documentation/fault-injection/fault-injection.txt +++ b/Documentation/fault-injection/fault-injection.txt @@ -15,6 +15,10 @@ o fail_page_alloc injects page allocation failures. (alloc_pages(), get_free_pages(), ...) +o fail_futex + + injects futex deadlock and uaddr fault errors. + o fail_make_request injects disk IO errors on devices permitted by setting @@ -113,6 +117,12 @@ configuration of fault-injection capabilities. specifies the minimum page allocation order to be injected failures. +- /sys/kernel/debug/fail_futex/ignore-private: + + Format: { 'Y' | 'N' } + default is 'N', setting it to 'Y' will disable failure injections + when dealing with private (address space) futexes. + o Boot option In order to inject faults while debugfs is not available (early boot time), @@ -121,6 +131,7 @@ use the boot option: failslab= fail_page_alloc= fail_make_request= + fail_futex= mmc_core.fail_request=<interval>,<probability>,<space>,<times> How to add new fault injection capability diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index eafa6a53f72c..2ba8461b0631 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -2327,9 +2327,7 @@ about the state (old or new) implies an SMP-conditional general memory barrier explicit lock operations, described later). These include: xchg(); - cmpxchg(); atomic_xchg(); atomic_long_xchg(); - atomic_cmpxchg(); atomic_long_cmpxchg(); atomic_inc_return(); atomic_long_inc_return(); atomic_dec_return(); atomic_long_dec_return(); atomic_add_return(); atomic_long_add_return(); @@ -2342,7 +2340,9 @@ explicit lock operations, described later). These include: test_and_clear_bit(); test_and_change_bit(); - /* when succeeds (returns 1) */ + /* when succeeds */ + cmpxchg(); + atomic_cmpxchg(); atomic_long_cmpxchg(); atomic_add_unless(); atomic_long_add_unless(); These are used for such things as implementing ACQUIRE-class and RELEASE-class diff --git a/Documentation/static-keys.txt b/Documentation/static-keys.txt index c4407a41b0fc..f4cb0b2d5cd7 100644 --- a/Documentation/static-keys.txt +++ b/Documentation/static-keys.txt @@ -1,7 +1,22 @@ Static Keys ----------- -By: Jason Baron <jbaron@redhat.com> +DEPRECATED API: + +The use of 'struct static_key' directly, is now DEPRECATED. In addition +static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following: + +struct static_key false = STATIC_KEY_INIT_FALSE; +struct static_key true = STATIC_KEY_INIT_TRUE; +static_key_true() +static_key_false() + +The updated API replacements are: + +DEFINE_STATIC_KEY_TRUE(key); +DEFINE_STATIC_KEY_FALSE(key); +static_key_likely() +statick_key_unlikely() 0) Abstract @@ -9,22 +24,22 @@ Static keys allows the inclusion of seldom used features in performance-sensitive fast-path kernel code, via a GCC feature and a code patching technique. A quick example: - struct static_key key = STATIC_KEY_INIT_FALSE; + DEFINE_STATIC_KEY_FALSE(key); ... - if (static_key_false(&key)) + if (static_branch_unlikely(&key)) do unlikely code else do likely code ... - static_key_slow_inc(); + static_branch_enable(&key); ... - static_key_slow_inc(); + static_branch_disable(&key); ... -The static_key_false() branch will be generated into the code with as little +The static_branch_unlikely() branch will be generated into the code with as little impact to the likely code path as possible. @@ -56,7 +71,7 @@ the branch site to change the branch direction. For example, if we have a simple branch that is disabled by default: - if (static_key_false(&key)) + if (static_branch_unlikely(&key)) printk("I am the true branch\n"); Thus, by default the 'printk' will not be emitted. And the code generated will @@ -75,68 +90,55 @@ the basis for the static keys facility. In order to make use of this optimization you must first define a key: - struct static_key key; - -Which is initialized as: - - struct static_key key = STATIC_KEY_INIT_TRUE; + DEFINE_STATIC_KEY_TRUE(key); or: - struct static_key key = STATIC_KEY_INIT_FALSE; + DEFINE_STATIC_KEY_FALSE(key); + -If the key is not initialized, it is default false. The 'struct static_key', -must be a 'global'. That is, it can't be allocated on the stack or dynamically +The key must be global, that is, it can't be allocated on the stack or dynamically allocated at run-time. The key is then used in code as: - if (static_key_false(&key)) + if (static_branch_unlikely(&key)) do unlikely code else do likely code Or: - if (static_key_true(&key)) + if (static_branch_likely(&key)) do likely code else do unlikely code -A key that is initialized via 'STATIC_KEY_INIT_FALSE', must be used in a -'static_key_false()' construct. Likewise, a key initialized via -'STATIC_KEY_INIT_TRUE' must be used in a 'static_key_true()' construct. A -single key can be used in many branches, but all the branches must match the -way that the key has been initialized. +Keys defined via DEFINE_STATIC_KEY_TRUE(), or DEFINE_STATIC_KEY_FALSE, may +be used in either static_branch_likely() or static_branch_unlikely() +statemnts. -The branch(es) can then be switched via: +Branch(es) can be set true via: - static_key_slow_inc(&key); - ... - static_key_slow_dec(&key); +static_branch_enable(&key); -Thus, 'static_key_slow_inc()' means 'make the branch true', and -'static_key_slow_dec()' means 'make the branch false' with appropriate -reference counting. For example, if the key is initialized true, a -static_key_slow_dec(), will switch the branch to false. And a subsequent -static_key_slow_inc(), will change the branch back to true. Likewise, if the -key is initialized false, a 'static_key_slow_inc()', will change the branch to -true. And then a 'static_key_slow_dec()', will again make the branch false. +or false via: + +static_branch_disable(&key); -An example usage in the kernel is the implementation of tracepoints: +The branch(es) can then be switched via reference counts: - static inline void trace_##name(proto) \ - { \ - if (static_key_false(&__tracepoint_##name.key)) \ - __DO_TRACE(&__tracepoint_##name, \ - TP_PROTO(data_proto), \ - TP_ARGS(data_args), \ - TP_CONDITION(cond)); \ - } + static_branch_inc(&key); + ... + static_branch_dec(&key); -Tracepoints are disabled by default, and can be placed in performance critical -pieces of the kernel. Thus, by using a static key, the tracepoints can have -absolutely minimal impact when not in use. +Thus, 'static_branch_inc()' means 'make the branch true', and +'static_branch_dec()' means 'make the branch false' with appropriate +reference counting. For example, if the key is initialized true, a +static_branch_dec(), will switch the branch to false. And a subsequent +static_branch_inc(), will change the branch back to true. Likewise, if the +key is initialized false, a 'static_branch_inc()', will change the branch to +true. And then a 'static_branch_dec()', will again make the branch false. 4) Architecture level code patching interface, 'jump labels' @@ -150,9 +152,12 @@ simply fall back to a traditional, load, test, and jump sequence. * #define JUMP_LABEL_NOP_SIZE, see: arch/x86/include/asm/jump_label.h -* __always_inline bool arch_static_branch(struct static_key *key), see: +* __always_inline bool arch_static_branch(struct static_key *key, bool branch), see: arch/x86/include/asm/jump_label.h +* __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch), + see: arch/x86/include/asm/jump_label.h + * void arch_jump_label_transform(struct jump_entry *entry, enum jump_label_type type), see: arch/x86/kernel/jump_label.c @@ -173,7 +178,7 @@ SYSCALL_DEFINE0(getppid) { int pid; -+ if (static_key_false(&key)) ++ if (static_branch_unlikely(&key)) + printk("I am the true branch\n"); rcu_read_lock(); |