[Git][ghc/ghc][wip/tsan/fix-races] 17 commits: Fix thunk update ordering

Ben Gamari (@bgamari) gitlab at gitlab.haskell.org
Wed Dec 13 21:04:06 UTC 2023 


Ben Gamari pushed to branch wip/tsan/fix-races at Glasgow Haskell Compiler / GHC


Commits:
f0682cb3 by Ben Gamari at 2023-12-13T16:02:24-05:00
Fix thunk update ordering

Previously we attempted to ensure soundness of concurrent thunk update
by synchronizing on the access of the thunk's info table pointer field.
This was believed to be sufficient since the indirectee (which may
expose a closure allocated by another core) would not be examined
until the info table pointer update is complete.

However, it turns out that this can result in data races in the presence
of multiple threads racing a update a single thunk. For instance,
consider this interleaving under the old scheme:

            Thread A                             Thread B
            ---------                            ---------
    t=0     Enter t
      1     Push update frame
      2     Begin evaluation

      4     Pause thread
      5     t.indirectee=tso
      6     Release t.info=BLACKHOLE

      7     ... (e.g. GC)

      8     Resume thread
      9     Finish evaluation
      10    Relaxed t.indirectee=x

      11                                         Load t.info
      12                                         Acquire fence
      13                                         Inspect t.indirectee

      14    Release t.info=BLACKHOLE

Here Thread A enters thunk `t` but is soon paused, resulting in `t`
being lazily blackholed at t=6. Then, at t=10 Thread A finishes
evaluation and updates `t.indirectee` with a relaxed store.

Meanwhile, Thread B enters the blackhole. Under the old scheme this
would introduce an acquire-fence but this would only synchronize with
Thread A at t=6. Consequently, the result of the evaluation, `x`, is not
visible to Thread B, introducing a data race.

We fix this by treating the `indirectee` field as we do all other
mutable fields. This means we must always access this field with
acquire-loads and release-stores.

See #23185.

- - - - -
2763aa7a by Ben Gamari at 2023-12-13T16:03:55-05:00
rts: Fix data race in threadPaused

This only affects an assertion in the debug RTS and only needs relaxed
ordering.

- - - - -
6d23ae25 by Ben Gamari at 2023-12-13T16:03:55-05:00
cmm: Introduce MO_RelaxedRead

In hand-written Cmm it can sometimes be necessary to atomically load
from memory deep within an expression (e.g. see the `CHECK_GC` macro).
This MachOp provides a convenient way to do so without breaking the
expression into multiple statements.

- - - - -
301f14fd by Ben Gamari at 2023-12-13T16:03:55-05:00
codeGen: Use relaxed accesses in ticky bumping

- - - - -
0a72f699 by Ben Gamari at 2023-12-13T16:03:55-05:00
rts: Fix data race in Interpreter's preemption check

- - - - -
52b8d632 by Ben Gamari at 2023-12-13T16:03:55-05:00
rts: Fix data race in threadStatus#

- - - - -
2a31080f by Ben Gamari at 2023-12-13T16:03:55-05:00
base: use atomic write when updating timer manager

- - - - -
bcbebfac by Ben Gamari at 2023-12-13T16:03:55-05:00
Use relaxed atomics to manipulate TSO status fields

- - - - -
89050edf by Ben Gamari at 2023-12-13T16:03:55-05:00
rts: Add necessary barriers when manipulating TSO owner

- - - - -
7aa56933 by Ben Gamari at 2023-12-13T16:03:55-05:00
rts: Fix synchronization on thread blocking state

- - - - -
2595b0d9 by Ben Gamari at 2023-12-13T16:03:55-05:00
rts: Use relaxed ordering on dirty/clean info tables updates

When changing the dirty/clean state of a mutable object we needn't have
any particular ordering.

- - - - -
4f888bb5 by Ben Gamari at 2023-12-13T16:03:55-05:00
codeGen: Use relaxed-read in closureInfoPtr

- - - - -
843f3c3e by Ben Gamari at 2023-12-13T16:03:55-05:00
STM: Use acquire loads when possible

Full sequential consistency is not needed here.

- - - - -
f9f8c846 by Ben Gamari at 2023-12-13T16:03:55-05:00
rts/Messages: Fix data race

- - - - -
d6c509c7 by Ben Gamari at 2023-12-13T16:03:55-05:00
rts/Prof: Fix data race

- - - - -
39a6c2f9 by Ben Gamari at 2023-12-13T16:03:55-05:00
rts: Use fence rather than redundant load

Previously we would use an atomic load to ensure acquire ordering.
However, we now have `ACQUIRE_FENCE_ON`, which allows us to express this
more directly.

- - - - -
849b8b0d by Ben Gamari at 2023-12-13T16:03:55-05:00
rts: Fix data races in profiling timer

- - - - -


30 changed files:

- compiler/GHC/Cmm/Expr.hs
- compiler/GHC/Cmm/Info.hs
- compiler/GHC/Cmm/MachOp.hs
- compiler/GHC/Cmm/Parser.y
- compiler/GHC/Cmm/ThreadSanitizer.hs
- compiler/GHC/CmmToAsm/AArch64/CodeGen.hs
- compiler/GHC/CmmToAsm/PPC/CodeGen.hs
- compiler/GHC/CmmToAsm/Wasm/FromCmm.hs
- compiler/GHC/CmmToAsm/X86/CodeGen.hs
- compiler/GHC/CmmToC.hs
- compiler/GHC/CmmToLlvm/CodeGen.hs
- compiler/GHC/StgToCmm/Bind.hs
- compiler/GHC/StgToCmm/Ticky.hs
- compiler/GHC/StgToCmm/Utils.hs
- libraries/base/src/GHC/Event/Thread.hs
- rts/Apply.cmm
- rts/Compact.cmm
- rts/Exception.cmm
- rts/Heap.c
- rts/HeapStackCheck.cmm
- rts/Interpreter.c
- rts/Messages.c
- rts/PrimOps.cmm
- rts/Proftimer.c
- rts/RaiseAsync.c
- rts/STM.c
- rts/Schedule.c
- rts/StableName.c
- rts/StgMiscClosures.cmm
- rts/StgStartup.cmm


The diff was not included because it is too large.


View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/fa8aca8e0304056d9a1139da0de450eb2fc6be68...849b8b0de53f327d00479f994b816618423c5e40

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/fa8aca8e0304056d9a1139da0de450eb2fc6be68...849b8b0de53f327d00479f994b816618423c5e40
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