Hi,
I am building an AtomicCell primitive and encountered a Miri error about Stacked Borrows.
The error is generated for this test:
let fancy_cell = Arc::new(AtomicCell::new("Bonjour"));
(0..10).map( |_| {
let cell = fancy_cell.clone();
thread::spawn(move || {
for _ in 0..10 {
cell.store("Bonjour")}})
})
.collect::<Vec<_>>()
.into_iter()
.for_each(|h|{h.join();});
It produces this error:
error: Undefined Behavior: not granting access to tag <107473> because that would remove [Unique for <107062>] which is weakly protected because it is an argument of call 49781
- --> /redacted/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:3273:33*
-
|*
3273 | (SeqCst, SeqCst) => intrinsics::atomic_cxchg_seqcst_seqcst(dst, old, new),
-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not granting access to tag <107473> because that would remove [Unique for <107062>] which is weakly protected because it is an argument of call 49781*
It also produces this information about the tags:
<107473> was created by a SharedReadWrite retag at offsets [0x10..0x11]
- --> tests/con_test.rs:45:89*
-
|*
45 | (0..10).map(||{ let cell = fancy_cell.clone(); thread::spawn(move||{for _ in 0..10{cell.store("Bonjour")}})}).collect::<Vec<>>().into_iter().for_each(|h|{h.join();});
-
| ^^^^^^^^^^^^^^^^^^^^^*
<107062> is this argument
- --> tests/con_test.rs:45:89*
-
|*
45 | (0..10).map(||{ let cell = fancy_cell.clone(); thread::spawn(move||{for _ in 0..10{cell.store("Bonjour")}})}).collect::<Vec<>>().into_iter().for_each(|h|{h.join();});
-
| ^^^^^^^^^^^^^^^^^^^^^*
To me this reads like an aliasing issue? How could and would SharedReadWrite_Permissions be created/fix the error?
Strangely a single threaded test (calling the erroring function too) causes no errors:
let x = AtomicCell::new("Bonjour");
x.store("Bonjour");
x.store("Bonjour");
Works perfectly fine in Miris opinion.
Note:
Internally the pointers passed into the intrinsic function are loaded from AtomicPtrs which get their pointers from UnsafeCell::get();
The raw pointers pass function and thread boundaries.
About Stacked Borrows
Help is appreciated.
Thanks,
Elektron
