Messages in this thread | | | Date | Thu, 5 Dec 2013 10:50:42 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH tip/core/locking 4/4] Documentation/memory-barriers.txt: Document ACCESS_ONCE() |
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> + (*) The compiler is within its rights to reload a variable, for example, > + in cases where high register pressure prevents the compiler from > + keeping all data of interest in registers. The compiler might > + therefore optimize the variable tmp out of our previous example: > + > + while (tmp = a) > + do_something_with(tmp); > + > + This could result in the following code, which is perfectly safe in > + single-threaded code, but can be fatal in concurrent code: > + > + while (a) > + do_something_with(a); > + > + For example, the optimized version of this code could result in > + passing a zero to do_something_with() in the case where the variable > + a was modified by some other CPU between the "while" statement and > + the call to do_something_with().
Nit: I guess references to variable names such as 'a' should be quoted (same for 'tmp', 'b', etc):
For example, the optimized version of this code could result in passing a zero to do_something_with() in the case where the variable 'a' was modified by some other CPU between the "while" statement and the call to do_something_with().
which makes reading it less ambiguous and more fluid IMO. This observation applies to the whole document as 'a' is used in many places.
Thanks,
Ingo
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