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author | Paul Heidekrüger <paul.heidekrueger@in.tum.de> | 2022-09-03 16:57:17 +0000 |
---|---|---|
committer | Paul E. McKenney <paulmck@kernel.org> | 2022-10-18 15:14:52 -0700 |
commit | fc13b47692efdc829842757798011fa2e13eb9ff (patch) | |
tree | bafe71e70ad900c24b4d0d07b37f136c054723fa /tools | |
parent | 9abf2313adc1ca1b6180c508c25f22f9395cc780 (diff) | |
download | linux-stable-fc13b47692efdc829842757798011fa2e13eb9ff.tar.gz linux-stable-fc13b47692efdc829842757798011fa2e13eb9ff.tar.bz2 linux-stable-fc13b47692efdc829842757798011fa2e13eb9ff.zip |
tools/memory-model: Weaken ctrl dependency definition in explanation.txt
The current informal control dependency definition in explanation.txt is
too broad and, as discussed, needs to be updated.
Consider the following example:
> if(READ_ONCE(x))
> return 42;
>
> WRITE_ONCE(y, 42);
>
> return 21;
The read event determines whether the write event will be executed "at all"
- as per the current definition - but the formal LKMM does not recognize
this as a control dependency.
Introduce a new definition which includes the requirement for the second
memory access event to syntactically lie within the arm of a non-loop
conditional.
Link: https://lore.kernel.org/all/20220615114330.2573952-1-paul.heidekrueger@in.tum.de/
Cc: Marco Elver <elver@google.com>
Cc: Charalampos Mainas <charalampos.mainas@gmail.com>
Cc: Pramod Bhatotia <pramod.bhatotia@in.tum.de>
Cc: Soham Chakraborty <s.s.chakraborty@tudelft.nl>
Cc: Martin Fink <martin.fink@in.tum.de>
Co-developed-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul Heidekrüger <paul.heidekrueger@in.tum.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'tools')
-rw-r--r-- | tools/memory-model/Documentation/explanation.txt | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/tools/memory-model/Documentation/explanation.txt b/tools/memory-model/Documentation/explanation.txt index ee819a402b69..11a1d2d4f681 100644 --- a/tools/memory-model/Documentation/explanation.txt +++ b/tools/memory-model/Documentation/explanation.txt @@ -464,9 +464,10 @@ to address dependencies, since the address of a location accessed through a pointer will depend on the value read earlier from that pointer. -Finally, a read event and another memory access event are linked by a -control dependency if the value obtained by the read affects whether -the second event is executed at all. Simple example: +Finally, a read event X and a write event Y are linked by a control +dependency if Y syntactically lies within an arm of an if statement and +X affects the evaluation of the if condition via a data or address +dependency (or similarly for a switch statement). Simple example: int x, y; |