Memory leak in `@tailwindcss/oxide` — RSS grows 0 → 15 GB in 12 seconds, reproduces with both `next build` and `@tailwindcss/cli` standalone (Tailwind v4.3.3)

## Summary

The `@tailwindcss/oxide` Rust binary used by Tailwind v4 (via `@tailwindcss/postcss` and `@tailwindcss/cli`) exhibits unbounded memory growth when processing any input containing `@import "tailwindcss";`. RSS climbs from ~0 to ~15 GB in 12–60 seconds and is killed by `SIGKILL`. This is **not** a Turbopack or Next.js issue — we reproduced the same OOM with the standalone `@tailwindcss/cli`, which is the official supported build path. The leak is in Oxide itself.

## Two independent reproductions, identical OOM signature

### Repro A: `next build` (via `@tailwindcss/postcss`)

`next build` (Turbopack) spawns a PostCSS worker that invokes `@tailwindcss/postcss`, which calls Oxide. Worker RSS grows 30 MB → 15 GB in 56 seconds.

### Repro B: `@tailwindcss/cli` (standalone, no Next.js involved)

The official Tailwind CLI invokes Oxide directly with no Next.js, no Turbopack, no PostCSS, no bundler. RSS grows 0 → 15 GB in 12 seconds, then `SIGKILL` (exit 137).

This proves the bug is in Oxide, not in Next.js or any integration layer.

## Memory profile (Repro B — `@tailwindcss/cli`)

Host state immediately before compile: 15 GB available RAM, no other Node processes running.

Memory monitor sampled every 2 seconds during `tailwindcss -i ./src/app/globals.css -o /tmp/generated.css`:

| Elapsed | Available RAM | Top process RSS | Process |
|--------:|---------------:|-----------------:|---------|
| 0 s | 15108 MB | 276 MB | next-server (unrelated) |
| 2 s | 14066 MB | 1168 MB | **node** (CLI startup) |
| 4 s | 10850 MB | 4386 MB | node |
| 6 s | 7984 MB | 7239 MB | node |
| 8 s | 4228 MB | 10975 MB | node |
| 10 s | 1260 MB | 13974 MB | node |
| 12 s | 619 MB | 14618 MB | node |
| 14 s | 63 MB | 15170 MB | node ← **SIGKILL** |

Growth rate: ~1.7 GB per 2 seconds — consistent with unbounded AST/scan allocation without release, not a slow leak.

## Memory profile (Repro A — `next build`)

Same host, same `globals.css`, same 15 GB free before build. Sampled every 5 seconds:

| Elapsed | Available RAM | Top process RSS | Process |
|--------:|---------------:|-----------------:|---------|
| 0 s | 15433 MB | 30 MB | caddy (unrelated) |
| 5 s | 14721 MB | 1404 MB | next-build |
| 20 s | 13057 MB | 2106 MB | next-build |
| 25 s | 3032 MB | 5674 MB | **node** (PostCSS worker spawned) |
| 56 s | 28 MB | 15198 MB | node ← **SIGKILL** |
| 65 s | 15271 MB | 275 MB | next-build (parent retries) |

The PostCSS worker is a child process of `next-build`:
```
next-build (v16.3.1)
└─ node ./.next/build/chunks/pool_entry-[turbopack-node]_transforms_postcss_ts_0tp-k2v._.js
```

The worker file name (`transforms_postcss_ts`) confirms it is the PostCSS transform pipeline, which calls `@tailwindcss/postcss`, which calls Oxide.

## Reproduction

### Repro B (simplest — no Next.js required)

**`package.json`** (relevant deps)
```json
{
  "devDependencies": {
    "tailwindcss": "4.3.3",
    "@tailwindcss/cli": "4.3.3"
  }
}
```

**`globals.css`** (23 bytes — minimum that triggers the issue)
```css
@import "tailwindcss";
```

**Command**
```bash
npx @tailwindcss/cli -i ./globals.css -o ./generated.css
```

**Expected:** compile completes, RSS stays bounded (a few hundred MB at most).

**Actual:** RSS climbs 0 → 15 GB in 12 seconds, killed by `SIGKILL` (exit 137).

### Repro A (Next.js 16 + Turbopack)

**`src/app/layout.tsx`**
```tsx
import './globals.css'

export default function RootLayout({ children }: { children: React.ReactNode }) {
  return (
    <html lang="en">
      <body>{children}</body>
    </html>
  )
}
```

**`src/app/globals.css`** (23 bytes)
```css
@import "tailwindcss";
```

**`postcss.config.js`**
```js
module.exports = {
  plugins: {
    "@tailwindcss/postcss": {},
  },
}
```

**Command**
```bash
npx next build
```

**Actual:** PostCSS worker RSS climbs 0 → 15 GB in 56 seconds, killed by `SIGKILL`.

## Environment

| Component | Version |
|-----------|---------|
| Tailwind CSS | 4.3.3 |
| @tailwindcss/postcss | 4.3.3 |
| @tailwindcss/cli | 4.3.3 |
| @tailwindcss/oxide-linux-x64-gnu | 4.3.3 |
| Node.js | v22.x (also tested on v20.20.2 — same issue) |
| OS | Ubuntu 22.04 (kernel 5.15), x86_64, glibc 2.35 |

## Diagnostic findings

### 1. Even a 23-byte input triggers the leak

`@import "tailwindcss";` alone is sufficient. Custom CSS, `@theme inline`, `@source` directives, and project-specific utility classes are **not** required. The leak is triggered by Oxide's bootstrap, not by user-authored CSS.

### 2. Not resource contention

Tested with all production services stopped (pm2 Next.js + 8 systemd microservices), 15 GB available RAM, no other Node processes running. The CLI still OOMed at the same RSS ceiling.

### 3. Tailwind v3 syntax works on the same machine

Replacing `globals.css` with v3 syntax (`@tailwind base; @tailwind components; @tailwind utilities;`) makes the build complete successfully with stable memory (~2 GB peak).

### 4. Not a musl/glibc binary mismatch

Two Oxide native packages were installed (`@tailwindcss/oxide-linux-x64-gnu` and `@tailwindcss/oxide-linux-x64-musl`). Removing the musl binary does not resolve the issue. The host is glibc 2.35.

### 5. Not a Next.js or Turbopack bug

Repro B reproduces the OOM without any Next.js, Turbopack, or bundler involvement. The leak is in `@tailwindcss/oxide` itself, invoked through `@tailwindcss/cli`.

## Workaround

We have not found a workaround that allows Tailwind v4 to compile on hosts with less than ~32 GB RAM. Current mitigations:

1. **Build on a separate machine** with ≥32 GB RAM and deploy the artifact (rsync `.next` or generated CSS) to production.
2. **Downgrade to Tailwind v3** — works on the same host with stable memory.

## Why we're filing this

This issue makes Tailwind v4 effectively unusable on standard 16 GB VPS hosts — a very common deployment target — regardless of whether the user is using Next.js, Turbopack, or the standalone CLI. The growth pattern (0 → 15 GB in 12 seconds on a 23-byte input) is consistent with an unbounded allocation bug in Oxide's bootstrap path, and we believe it is actionable upstream.

## Reproduction repo

A fresh project with `npm install tailwindcss @tailwindcss/cli` + the 23-byte `globals.css` reproduces the issue. No application code, no framework, no bundler required.

## Tags

`area: oxide`, `area: cli`, `area: postcss`, `type: bug`, `severity: blocker`

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Uh oh!

Memory leak in `@tailwindcss/oxide` — RSS grows 0 → 15 GB in 12 seconds, reproduces with both `next build` and `@tailwindcss/cli` standalone (Tailwind v4.3.3) #20464

Summary

Two independent reproductions, identical OOM signature

Repro A: `next build` (via `@tailwindcss/postcss`)

Repro B: `@tailwindcss/cli` (standalone, no Next.js involved)

Memory profile (Repro B — `@tailwindcss/cli`)

Memory profile (Repro A — `next build`)

Reproduction

Repro B (simplest — no Next.js required)

Repro A (Next.js 16 + Turbopack)

Environment

Diagnostic findings

1. Even a 23-byte input triggers the leak

2. Not resource contention

3. Tailwind v3 syntax works on the same machine

4. Not a musl/glibc binary mismatch

5. Not a Next.js or Turbopack bug

Workaround

Why we're filing this

Reproduction repo

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Elapsed	Available RAM	Top process RSS	Process
0 s	15108 MB	276 MB	next-server (unrelated)
2 s	14066 MB	1168 MB	node (CLI startup)
4 s	10850 MB	4386 MB	node
6 s	7984 MB	7239 MB	node
8 s	4228 MB	10975 MB	node
10 s	1260 MB	13974 MB	node
12 s	619 MB	14618 MB	node
14 s	63 MB	15170 MB	node ← SIGKILL

Elapsed	Available RAM	Top process RSS	Process
0 s	15433 MB	30 MB	caddy (unrelated)
5 s	14721 MB	1404 MB	next-build
20 s	13057 MB	2106 MB	next-build
25 s	3032 MB	5674 MB	node (PostCSS worker spawned)
56 s	28 MB	15198 MB	node ← SIGKILL
65 s	15271 MB	275 MB	next-build (parent retries)

Component	Version
Tailwind CSS	4.3.3
@tailwindcss/postcss	4.3.3
@tailwindcss/cli	4.3.3
@tailwindcss/oxide-linux-x64-gnu	4.3.3
Node.js	v22.x (also tested on v20.20.2 — same issue)
OS	Ubuntu 22.04 (kernel 5.15), x86_64, glibc 2.35

Uh oh!

Uh oh!

Memory leak in @tailwindcss/oxide — RSS grows 0 → 15 GB in 12 seconds, reproduces with both next build and @tailwindcss/cli standalone (Tailwind v4.3.3) #20464

Description

Summary

Two independent reproductions, identical OOM signature

Repro A: next build (via @tailwindcss/postcss)

Repro B: @tailwindcss/cli (standalone, no Next.js involved)

Memory profile (Repro B — @tailwindcss/cli)

Memory profile (Repro A — next build)

Reproduction

Repro B (simplest — no Next.js required)

Repro A (Next.js 16 + Turbopack)

Environment

Diagnostic findings

1. Even a 23-byte input triggers the leak

2. Not resource contention

3. Tailwind v3 syntax works on the same machine

4. Not a musl/glibc binary mismatch

5. Not a Next.js or Turbopack bug

Workaround

Why we're filing this

Reproduction repo

Tags

Activity

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

Memory leak in `@tailwindcss/oxide` — RSS grows 0 → 15 GB in 12 seconds, reproduces with both `next build` and `@tailwindcss/cli` standalone (Tailwind v4.3.3) #20464

Repro A: `next build` (via `@tailwindcss/postcss`)

Repro B: `@tailwindcss/cli` (standalone, no Next.js involved)

Memory profile (Repro B — `@tailwindcss/cli`)

Memory profile (Repro A — `next build`)