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Diffstat (limited to 'Documentation/core-api/atomic_ops.rst')
| -rw-r--r-- | Documentation/core-api/atomic_ops.rst | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/Documentation/core-api/atomic_ops.rst b/Documentation/core-api/atomic_ops.rst index fce929144ccd..724583453e1f 100644 --- a/Documentation/core-api/atomic_ops.rst +++ b/Documentation/core-api/atomic_ops.rst @@ -29,7 +29,7 @@ updated by one CPU, local_t is probably more appropriate. Please see local_t. The first operations to implement for atomic_t's are the initializers and -plain reads. :: +plain writes. :: #define ATOMIC_INIT(i) { (i) } #define atomic_set(v, i) ((v)->counter = (i)) @@ -111,7 +111,6 @@ If the compiler can prove that do_something() does not store to the variable a, then the compiler is within its rights transforming this to the following:: - tmp = a; if (a > 0) for (;;) do_something(); @@ -119,7 +118,7 @@ the following:: If you don't want the compiler to do this (and you probably don't), then you should use something like the following:: - while (READ_ONCE(a) < 0) + while (READ_ONCE(a) > 0) do_something(); Alternatively, you could place a barrier() call in the loop. @@ -467,10 +466,12 @@ Like the above, except that these routines return a boolean which indicates whether the changed bit was set _BEFORE_ the atomic bit operation. -WARNING! It is incredibly important that the value be a boolean, -ie. "0" or "1". Do not try to be fancy and save a few instructions by -declaring the above to return "long" and just returning something like -"old_val & mask" because that will not work. + +.. warning:: + It is incredibly important that the value be a boolean, ie. "0" or "1". + Do not try to be fancy and save a few instructions by declaring the + above to return "long" and just returning something like "old_val & + mask" because that will not work. For one thing, this return value gets truncated to int in many code paths using these interfaces, so on 64-bit if the bit is set in the |