Rc/Arc: don't leak the allocation if drop panics #132231

lukas-code · 2024-10-27T17:48:31Z

Currently, when the last Rc<T> or Arc<T> is dropped and the destructor of T panics, the allocation will be leaked. This leak is unnecessary since the data cannot be (safely) accessed again and Box already deallocates in this case, so let's do the same for Rc and Arc, too.

rustbot · 2024-10-27T17:48:40Z

r? @tgross35

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tgross35 · 2024-10-27T21:25:53Z

library/alloc/src/rc.rs

+
+                // Destroy the contained object.
+                // We cannot use `get_mut_unchecked` here, because `self.alloc` is borrowed.
+                ptr::drop_in_place(&mut (*self.ptr.as_ptr()).value);


Could this just use raw mut?

ptr::drop_in_place(&raw mut self.ptr.as_ptr().value);

As far as I understand, drop_in_place always works as if it's argument was &mut T and only uses *mut T in the signature for compatibility reasons (see #103957 and #111807).

So, yes, this could use &raw mut, but the pointer would just automatically be reborrowed as a reference anyway, so i used &mut directly for clarity.

Makes sense, thanks for the follow up

tgross35 · 2024-10-27T21:32:19Z

I don't really expect anything here but just in case the drop path changes are sensitive somehow:

@bors try @rust-timer queue

bors · 2024-10-27T21:33:30Z

⌛ Trying commit 4a71a59 with merge 48c9fdd...

bors · 2024-10-27T23:23:29Z

☀️ Try build successful - checks-actions
Build commit: 48c9fdd (48c9fdd2bf3f86220bdf68cf602e42d7f9e0c4b5)

rust-timer · 2024-10-28T01:14:37Z

Finished benchmarking commit (48c9fdd): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	1.5%	[0.8%, 2.6%]	7
Improvements ✅ (primary)	-0.9%	[-1.3%, -0.2%]	3
Improvements ✅ (secondary)	-1.5%	[-1.5%, -1.5%]	1
All ❌✅ (primary)	-0.6%	[-1.3%, 0.3%]	4

Max RSS (memory usage)

Results (primary 2.5%, secondary 3.0%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	5.0%	[2.9%, 7.9%]	3
Regressions ❌ (secondary)	3.0%	[1.4%, 4.5%]	2
Improvements ✅ (primary)	-5.3%	[-5.3%, -5.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.5%	[-5.3%, 7.9%]	4

Cycles

Results (primary -1.0%, secondary 0.4%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.8%	[2.4%, 3.2%]	3
Improvements ✅ (primary)	-1.0%	[-1.0%, -1.0%]	1
Improvements ✅ (secondary)	-6.9%	[-6.9%, -6.9%]	1
All ❌✅ (primary)	-1.0%	[-1.0%, -1.0%]	1

Binary size

Results (primary 0.0%, secondary 0.5%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.3%]	25
Regressions ❌ (secondary)	0.5%	[0.0%, 4.0%]	43
Improvements ✅ (primary)	-0.1%	[-0.3%, -0.0%]	21
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-0.3%, 0.3%]	46

Bootstrap: 782.673s -> 783.739s (0.14%)
Artifact size: 333.75 MiB -> 333.75 MiB (0.00%)

tgross35 · 2024-10-28T17:34:16Z

The main regression is regression-31157 which is a pretty tiny crate doing parsing things, added to test a huge regression. I think that is acceptable given this is a nice usability improvement (especially Arc considering the useccase is probably to leak memory and continue) but just to see, could you test adding #[inline] to Rc's drop? Arc's drop has it already, thinking maybe it would reduce a call now that deallocate happens elsewhere.

lukas-code · 2024-10-28T22:02:14Z

Applied the same inline/outline trick from Arc to Rc. Let's see if this helps at all:

@bors try @rust-timer queue

bors · 2024-10-28T22:03:25Z

⌛ Trying commit 02ee639 with merge 01c529d...

bors · 2024-10-28T23:53:52Z

☀️ Try build successful - checks-actions
Build commit: 01c529d (01c529df780282284b312a27a6aaaddae3b6602f)

rust-timer · 2024-10-29T01:10:33Z

Finished benchmarking commit (01c529d): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.9%, 0.9%]	1
Regressions ❌ (secondary)	2.2%	[1.1%, 3.5%]	6
Improvements ✅ (primary)	-0.8%	[-1.6%, -0.2%]	4
Improvements ✅ (secondary)	-0.5%	[-0.6%, -0.3%]	7
All ❌✅ (primary)	-0.4%	[-1.6%, 0.9%]	5

Max RSS (memory usage)

Results (primary -0.7%, secondary 2.9%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	4.2%	[4.2%, 4.2%]	1
Regressions ❌ (secondary)	2.9%	[2.4%, 3.4%]	2
Improvements ✅ (primary)	-5.5%	[-5.5%, -5.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.7%	[-5.5%, 4.2%]	2

Cycles

Results (primary 0.0%, secondary 3.7%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.2%	[1.2%, 1.2%]	1
Regressions ❌ (secondary)	3.7%	[3.2%, 4.2%]	3
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-1.1%, 1.2%]	2

Binary size

Results (primary 0.0%, secondary 1.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.2%]	23
Regressions ❌ (secondary)	1.1%	[0.0%, 8.7%]	43
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.0%]	20
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-0.1%, 0.2%]	43

Bootstrap: 782.325s -> 785.165s (0.36%)
Artifact size: 333.64 MiB -> 333.76 MiB (0.04%)

tgross35 · 2024-10-29T01:23:22Z

There probably isn't too much to be done regarding perf, all of the regressions come from one small crate. The code changes look good to me.

@bors r+

bors · 2024-10-29T01:23:25Z

📌 Commit 02ee639 has been approved by tgross35

It is now in the queue for this repository.

bors · 2024-10-29T16:26:07Z

⌛ Testing commit 02ee639 with merge e473783...

bors · 2024-10-29T19:23:53Z

☀️ Test successful - checks-actions
Approved by: tgross35
Pushing e473783 to master...

rust-timer · 2024-10-29T22:32:59Z

Finished benchmarking commit (e473783): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

If the regression was expected or you think it can be justified,
please write a comment with sufficient written justification, and add
@rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
If you think that you know of a way to resolve the regression, try to create
a new PR with a fix for the regression.
If you do not understand the regression or you think that it is just noise,
you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.6%, 0.6%]	1
Regressions ❌ (secondary)	2.3%	[1.1%, 3.5%]	6
Improvements ✅ (primary)	-0.9%	[-1.4%, -0.3%]	3
Improvements ✅ (secondary)	-0.4%	[-0.6%, -0.2%]	5
All ❌✅ (primary)	-0.5%	[-1.4%, 0.6%]	4

Max RSS (memory usage)

Results (primary -1.4%, secondary 2.6%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	3.7%	[3.0%, 4.4%]	2
Regressions ❌ (secondary)	2.6%	[2.6%, 2.6%]	1
Improvements ✅ (primary)	-3.9%	[-5.9%, -1.7%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.4%	[-5.9%, 4.4%]	6

Cycles

Results (primary 1.3%, secondary 0.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.1%	[1.9%, 2.3%]	3
Regressions ❌ (secondary)	3.1%	[2.2%, 3.9%]	5
Improvements ✅ (primary)	-1.2%	[-1.2%, -1.2%]	1
Improvements ✅ (secondary)	-2.7%	[-3.1%, -2.3%]	5
All ❌✅ (primary)	1.3%	[-1.2%, 2.3%]	4

Binary size

Results (primary 0.0%, secondary 1.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.3%]	27
Regressions ❌ (secondary)	1.1%	[0.0%, 8.8%]	43
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	20
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-0.2%, 0.3%]	47

Bootstrap: 784.701s -> 784.999s (0.04%)
Artifact size: 333.58 MiB -> 333.64 MiB (0.02%)

rylev · 2024-11-05T20:17:05Z

Marking as triaged based on the analysis here

@rustbot label: +perf-regression-triaged

Lukas Markeffsky added 2 commits October 27, 2024 18:32

add test for panicking drop in Box/Rc/Arc

8a9f400

Rc/Arc: don't leak the allocation if drop panics

4a71a59

rustbot assigned tgross35 Oct 27, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 27, 2024

tgross35 reviewed Oct 27, 2024

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Oct 28, 2024

Rc destructor: tweak inlining

02ee639

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 29, 2024

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 29, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label Oct 29, 2024

bors merged commit e473783 into rust-lang:master Oct 29, 2024
7 checks passed

rustbot added this to the 1.84.0 milestone Oct 29, 2024

lukas-code deleted the rc-plug-leaks branch October 29, 2024 19:47

rustbot added the perf-regression-triaged The performance regression has been triaged. label Nov 5, 2024

Rc/Arc: don't leak the allocation if drop panics #132231

Rc/Arc: don't leak the allocation if drop panics #132231

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Overall result: ❌✅ regressions and improvements - please read the text below

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Overall result: ❌✅ regressions and improvements - please read the text below

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Overall result: ❌✅ regressions and improvements - please read the text below

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