path: root/Documentation
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authorLinus Torvalds <torvalds@linux-foundation.org>2020-02-04 07:24:48 +0000
committerLinus Torvalds <torvalds@linux-foundation.org>2020-02-04 07:24:48 +0000
commitcc12071ff39060fc2e47c58b43e249fe0d0061ee (patch)
tree085789dec88100d2ac12d9f2c990c00b909d7ee2 /Documentation
parent9717c1cea16e3eae81ca226f4c3670bb799b61ad (diff)
parentf3cc4e1d44a813a0685f2e558b78ace3db559722 (diff)
Merge branch 'akpm' (patches from Andrew)
Merge more updates from Andrew Morton: "The rest of MM and the rest of everything else: hotfixes, ipc, misc, procfs, lib, cleanups, arm" * emailed patches from Andrew Morton <akpm@linux-foundation.org>: (67 commits) ARM: dma-api: fix max_pfn off-by-one error in __dma_supported() treewide: remove redundant IS_ERR() before error code check include/linux/cpumask.h: don't calculate length of the input string lib: new testcases for bitmap_parse{_user} lib: rework bitmap_parse() lib: make bitmap_parse_user a wrapper on bitmap_parse lib: add test for bitmap_parse() bitops: more BITS_TO_* macros lib/string: add strnchrnul() proc: convert everything to "struct proc_ops" proc: decouple proc from VFS with "struct proc_ops" asm-generic/tlb: provide MMU_GATHER_TABLE_FREE asm-generic/tlb: rename HAVE_MMU_GATHER_NO_GATHER asm-generic/tlb: rename HAVE_MMU_GATHER_PAGE_SIZE asm-generic/tlb: rename HAVE_RCU_TABLE_FREE asm-generic/tlb: add missing CONFIG symbol asm-gemeric/tlb: remove stray function declarations asm-generic/tlb: avoid potential double flush mm/mmu_gather: invalidate TLB correctly on batch allocation failure and flush powerpc/mmu_gather: enable RCU_TABLE_FREE even for !SMP case ...
Diffstat (limited to 'Documentation')
1 files changed, 10 insertions, 6 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index ec3b5865c1be..7146da061693 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1868,12 +1868,16 @@ There are some more advanced barrier functions:
(*) smp_mb__before_atomic();
(*) smp_mb__after_atomic();
- These are for use with atomic (such as add, subtract, increment and
- decrement) functions that don't return a value, especially when used for
- reference counting. These functions do not imply memory barriers.
- These are also used for atomic bitop functions that do not return a
- value (such as set_bit and clear_bit).
+ These are for use with atomic RMW functions that do not imply memory
+ barriers, but where the code needs a memory barrier. Examples for atomic
+ RMW functions that do not imply are memory barrier are e.g. add,
+ subtract, (failed) conditional operations, _relaxed functions,
+ but not atomic_read or atomic_set. A common example where a memory
+ barrier may be required is when atomic ops are used for reference
+ counting.
+ These are also used for atomic RMW bitop functions that do not imply a
+ memory barrier (such as set_bit and clear_bit).
As an example, consider a piece of code that marks an object as being dead
and then decrements the object's reference count: