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mitigate ABA with 32-bit queue indices if possible #5042

Merged
merged 5 commits into from
Sep 27, 2022
Merged

mitigate ABA with 32-bit queue indices if possible #5042

merged 5 commits into from
Sep 27, 2022

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sbarral
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@sbarral sbarral commented Sep 21, 2022

When 64-bit atomics are supported, use 32-bit queue indices. This greatly improves resilience to ABA and has no impact on performance on 64-bit platforms.

Fixes: #5041

Motivation

Currently, a stealer preempted at the wrong moment could attempt to steal more tasks than are available in the queue, resulting in UB. This is due to a potential ABA where the stealer head wraps around due to many push/pop cycles, leading the stealer to wrongly conclude that the state of the queue has not changed.

Solution

The proposed solution is to strongly improve ABA resilience by using 32-bit instead of 16-bit buffer indices when possible.

At the moment, "when possible" is determined based on the availability of 64-bit atomics, as reported by the cfg_has_atomic_u64 macro. Another solution would be to use cfg(target_pointer_width = "64") to exclude 32-bit targets that support 64-bit atomics natively, such as armv7, since these targets may see an impact in performance.

No performance regression was observed on local tests on a x86_64 target using the rt_multi_threaded benchmark.

When 64-bit atomics are supported, use 32-bit queue indices. This
greatly improves resilience to ABA and has no impact on performance on
64-bit platforms.

Fixes: #5041
@github-actions github-actions bot added the R-loom Run loom tests on this PR label Sep 21, 2022
@Darksonn Darksonn added A-tokio Area: The main tokio crate M-runtime Module: tokio/runtime labels Sep 22, 2022
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In general this looks fine.

tokio/src/runtime/scheduler/multi_thread/queue.rs Outdated Show resolved Hide resolved
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Please merge master into your branch to fix the CI issues.

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Nevermind, I could do it myself.

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Thanks.

@Darksonn Darksonn enabled auto-merge (squash) September 27, 2022 21:36
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You don't need to add any more merge commits at this point.

@Darksonn Darksonn merged commit 78fc940 into tokio-rs:master Sep 27, 2022
dbischof90 pushed a commit to dbischof90/tokio that referenced this pull request Oct 1, 2022
…rs#5042)

When 64-bit atomics are supported, use 32-bit queue indices. This
greatly improves resilience to ABA and has no impact on performance on
64-bit platforms.

Fixes: tokio-rs#5041
crapStone pushed a commit to Calciumdibromid/CaBr2 that referenced this pull request Nov 22, 2022
This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [tokio](https://tokio.rs) ([source](https://github.com/tokio-rs/tokio)) | dependencies | minor | `1.21.2` -> `1.22.0` |
| [tokio](https://tokio.rs) ([source](https://github.com/tokio-rs/tokio)) | dev-dependencies | minor | `1.21.2` -> `1.22.0` |

---

### Release Notes

<details>
<summary>tokio-rs/tokio</summary>

### [`v1.22.0`](https://github.com/tokio-rs/tokio/releases/tag/tokio-1.22.0): Tokio v1.22.0

[Compare Source](tokio-rs/tokio@tokio-1.21.2...tokio-1.22.0)

##### Added

-   runtime: add `Handle::runtime_flavor` ([#&#8203;5138])
-   sync: add `Mutex::blocking_lock_owned` ([#&#8203;5130])
-   sync: add `Semaphore::MAX_PERMITS` ([#&#8203;5144])
-   sync: add `merge()` to semaphore permits ([#&#8203;4948])
-   sync: add `mpsc::WeakUnboundedSender` ([#&#8203;5189])

##### Added (unstable)

-   process: add `Command::process_group` ([#&#8203;5114])
-   runtime: export metrics about the blocking thread pool ([#&#8203;5161])
-   task: add `task::id()` and `task::try_id()` ([#&#8203;5171])

##### Fixed

-   macros: don't take ownership of futures in macros ([#&#8203;5087])
-   runtime: fix Stacked Borrows violation in `LocalOwnedTasks` ([#&#8203;5099])
-   runtime: mitigate ABA with 32-bit queue indices when possible ([#&#8203;5042])
-   task: wake local tasks to the local queue when woken by the same thread ([#&#8203;5095])
-   time: panic in release mode when `mark_pending` called illegally ([#&#8203;5093])
-   runtime: fix typo in expect message ([#&#8203;5169])
-   runtime: fix `unsync_load` on atomic types ([#&#8203;5175])
-   task: elaborate safety comments in task deallocation ([#&#8203;5172])
-   runtime: fix `LocalSet` drop in thread local ([#&#8203;5179])
-   net: remove libc type leakage in a public API ([#&#8203;5191])
-   runtime: update the alignment of `CachePadded` ([#&#8203;5106])

##### Changed

-   io: make `tokio::io::copy` continue filling the buffer when writer stalls ([#&#8203;5066])
-   runtime: remove `coop::budget` from `LocalSet::run_until` ([#&#8203;5155])
-   sync: make `Notify` panic safe ([#&#8203;5154])

##### Documented

-   io: fix doc for `write_i8` to use signed integers ([#&#8203;5040])
-   net: fix doc typos for TCP and UDP `set_tos` methods ([#&#8203;5073])
-   net: fix function name in `UdpSocket::recv` documentation ([#&#8203;5150])
-   sync: typo in `TryLockError` for `RwLock::try_write` ([#&#8203;5160])
-   task: document that spawned tasks execute immediately ([#&#8203;5117])
-   time: document return type of `timeout` ([#&#8203;5118])
-   time: document that `timeout` checks only before poll ([#&#8203;5126])
-   sync: specify return type of `oneshot::Receiver` in docs ([#&#8203;5198])

##### Internal changes

-   runtime: use const `Mutex::new` for globals ([#&#8203;5061])
-   runtime: remove `Option` around `mio::Events` in io driver ([#&#8203;5078])
-   runtime: remove a conditional compilation clause ([#&#8203;5104])
-   runtime: remove a reference to internal time handle ([#&#8203;5107])
-   runtime: misc time driver cleanup ([#&#8203;5120])
-   runtime: move signal driver to runtime module ([#&#8203;5121])
-   runtime: signal driver now uses I/O driver directly ([#&#8203;5125])
-   runtime: start decoupling I/O driver and I/O handle ([#&#8203;5127])
-   runtime: switch `io::handle` refs with scheduler:Handle ([#&#8203;5128])
-   runtime: remove Arc from I/O driver ([#&#8203;5134])
-   runtime: use signal driver handle via `scheduler::Handle` ([#&#8203;5135])
-   runtime: move internal clock fns out of context ([#&#8203;5139])
-   runtime: remove `runtime::context` module ([#&#8203;5140])
-   runtime: keep driver cfgs in `driver.rs` ([#&#8203;5141])
-   runtime: add `runtime::context` to unify thread-locals ([#&#8203;5143])
-   runtime: rename some confusing internal variables/fns ([#&#8203;5151])
-   runtime: move `coop` mod into `runtime` ([#&#8203;5152])
-   runtime: move budget state to context thread-local ([#&#8203;5157])
-   runtime: move park logic into runtime module ([#&#8203;5158])
-   runtime: move `Runtime` into its own file ([#&#8203;5159])
-   runtime: unify entering a runtime with `Handle::enter` ([#&#8203;5163])
-   runtime: remove handle reference from each scheduler ([#&#8203;5166])
-   runtime: move `enter` into `context` ([#&#8203;5167])
-   runtime: combine context and entered thread-locals ([#&#8203;5168])
-   runtime: fix accidental unsetting of current handle ([#&#8203;5178])
-   runtime: move `CoreStage` methods to `Core` ([#&#8203;5182])
-   sync: name mpsc semaphore types ([#&#8203;5146])

[#&#8203;4948]: tokio-rs/tokio#4948

[#&#8203;5040]: tokio-rs/tokio#5040

[#&#8203;5042]: tokio-rs/tokio#5042

[#&#8203;5061]: tokio-rs/tokio#5061

[#&#8203;5066]: tokio-rs/tokio#5066

[#&#8203;5073]: tokio-rs/tokio#5073

[#&#8203;5078]: tokio-rs/tokio#5078

[#&#8203;5087]: tokio-rs/tokio#5087

[#&#8203;5093]: tokio-rs/tokio#5093

[#&#8203;5095]: tokio-rs/tokio#5095

[#&#8203;5099]: tokio-rs/tokio#5099

[#&#8203;5104]: tokio-rs/tokio#5104

[#&#8203;5106]: tokio-rs/tokio#5106

[#&#8203;5107]: tokio-rs/tokio#5107

[#&#8203;5114]: tokio-rs/tokio#5114

[#&#8203;5117]: tokio-rs/tokio#5117

[#&#8203;5118]: tokio-rs/tokio#5118

[#&#8203;5120]: tokio-rs/tokio#5120

[#&#8203;5121]: tokio-rs/tokio#5121

[#&#8203;5125]: tokio-rs/tokio#5125

[#&#8203;5126]: tokio-rs/tokio#5126

[#&#8203;5127]: tokio-rs/tokio#5127

[#&#8203;5128]: tokio-rs/tokio#5128

[#&#8203;5130]: tokio-rs/tokio#5130

[#&#8203;5134]: tokio-rs/tokio#5134

[#&#8203;5135]: tokio-rs/tokio#5135

[#&#8203;5138]: tokio-rs/tokio#5138

[#&#8203;5138]: tokio-rs/tokio#5138

[#&#8203;5139]: tokio-rs/tokio#5139

[#&#8203;5140]: tokio-rs/tokio#5140

[#&#8203;5141]: tokio-rs/tokio#5141

[#&#8203;5143]: tokio-rs/tokio#5143

[#&#8203;5144]: tokio-rs/tokio#5144

[#&#8203;5144]: tokio-rs/tokio#5144

[#&#8203;5146]: tokio-rs/tokio#5146

[#&#8203;5150]: tokio-rs/tokio#5150

[#&#8203;5151]: tokio-rs/tokio#5151

[#&#8203;5152]: tokio-rs/tokio#5152

[#&#8203;5154]: tokio-rs/tokio#5154

[#&#8203;5155]: tokio-rs/tokio#5155

[#&#8203;5157]: tokio-rs/tokio#5157

[#&#8203;5158]: tokio-rs/tokio#5158

[#&#8203;5159]: tokio-rs/tokio#5159

[#&#8203;5160]: tokio-rs/tokio#5160

[#&#8203;5161]: tokio-rs/tokio#5161

[#&#8203;5163]: tokio-rs/tokio#5163

[#&#8203;5166]: tokio-rs/tokio#5166

[#&#8203;5167]: tokio-rs/tokio#5167

[#&#8203;5168]: tokio-rs/tokio#5168

[#&#8203;5169]: tokio-rs/tokio#5169

[#&#8203;5171]: tokio-rs/tokio#5171

[#&#8203;5172]: tokio-rs/tokio#5172

[#&#8203;5175]: tokio-rs/tokio#5175

[#&#8203;5178]: tokio-rs/tokio#5178

[#&#8203;5179]: tokio-rs/tokio#5179

[#&#8203;5182]: tokio-rs/tokio#5182

[#&#8203;5189]: tokio-rs/tokio#5189

[#&#8203;5191]: tokio-rs/tokio#5191

[#&#8203;5198]: tokio-rs/tokio#5198

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about these updates again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNC4yNy4xIiwidXBkYXRlZEluVmVyIjoiMzQuMjkuMiJ9-->

Co-authored-by: cabr2-bot <[email protected]>
Reviewed-on: https://codeberg.org/Calciumdibromid/CaBr2/pulls/1651
Reviewed-by: crapStone <[email protected]>
Co-authored-by: Calciumdibromid Bot <[email protected]>
Co-committed-by: Calciumdibromid Bot <[email protected]>
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