diff options
| -rw-r--r-- | Documentation/atomic_ops.txt | 18 |
1 files changed, 9 insertions, 9 deletions
diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt index 7281bf939779..6c5e8a9d2c6e 100644 --- a/Documentation/atomic_ops.txt +++ b/Documentation/atomic_ops.txt @@ -90,10 +90,10 @@ compiler optimizes the section accessing atomic_t variables. Properly aligned pointers, longs, ints, and chars (and unsigned equivalents) may be atomically loaded from and stored to in the same -sense as described for atomic_read() and atomic_set(). The ACCESS_ONCE() -macro should be used to prevent the compiler from using optimizations -that might otherwise optimize accesses out of existence on the one hand, -or that might create unsolicited accesses on the other. +sense as described for atomic_read() and atomic_set(). The READ_ONCE() +and WRITE_ONCE() macros should be used to prevent the compiler from using +optimizations that might otherwise optimize accesses out of existence on +the one hand, or that might create unsolicited accesses on the other. For example consider the following code: @@ -112,7 +112,7 @@ 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 (ACCESS_ONCE(a) < 0) + while (READ_ONCE(a) < 0) do_something(); Alternatively, you could place a barrier() call in the loop. @@ -141,7 +141,7 @@ of registers: reloading from variable a could save a flush to the stack and later reload. To prevent the compiler from attacking your code in this manner, write the following: - tmp_a = ACCESS_ONCE(a); + tmp_a = READ_ONCE(a); do_something_with(tmp_a); do_something_else_with(tmp_a); @@ -166,14 +166,14 @@ that expected b to never have the value 42 if a was zero. To prevent the compiler from doing this, write something like: if (a) - ACCESS_ONCE(b) = 9; + WRITE_ONCE(b, 9); else - ACCESS_ONCE(b) = 42; + WRITE_ONCE(b, 42); Don't even -think- about doing this without proper use of memory barriers, locks, or atomic operations if variable a can change at runtime! -*** WARNING: ACCESS_ONCE() DOES NOT IMPLY A BARRIER! *** +*** WARNING: READ_ONCE() OR WRITE_ONCE() DO NOT IMPLY A BARRIER! *** Now, we move onto the atomic operation interfaces typically implemented with the help of assembly code. |