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Fix advisory lock deadlock in sandbox creation pg_advisory_lock and pg_advisory_unlock used different pool connections, leaving locks permanently held. This caused sandbox creation to deadlock under concurrent requests. Replace with check_sandbox_cap that pins lock+count+unlock to a single connection. Remove now-unused advisory_lock/advisory_unlock functions.
Co-Authored-By
Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Author: Max J. <87768334+MaxJMath@users.noreply.github.com> · 2026-05-02 19:23 UTC
Commit: 63e5927c0c264fbc8140ff54fc00bf7dec25d553
Parent: 4d6d5db
2 files changed, +39 insertions, -24 deletions
M server/src/db/mod.rs +35 -14
@@ -71,20 +71,41 @@
71 71 use crate::error::Result;
72 72 use sqlx::PgPool;
73 73
74 - /// Acquire a session-level PostgreSQL advisory lock (blocks until available).
75 - pub async fn advisory_lock(pool: &PgPool, key: i64) -> Result<()> {
76 - sqlx::query("SELECT pg_advisory_lock($1)")
77 - .bind(key)
78 - .execute(pool)
79 - .await?;
80 - Ok(())
81 - }
74 + /// Check the sandbox per-IP cap under an advisory lock on a single connection.
75 + ///
76 + /// Acquires a session-level advisory lock, runs the count query, and unlocks —
77 + /// all on the same connection. Returns the active sandbox count.
78 + ///
79 + /// This avoids the bug where `advisory_lock` + `advisory_unlock` through a pool
80 + /// use different connections, leaving locks permanently held.
81 + pub async fn check_sandbox_cap(pool: &PgPool, lock_key: i64, ip: &str) -> Result<i64> {
82 + let mut conn = pool.acquire().await.map_err(|e| {
83 + crate::error::AppError::Internal(anyhow::anyhow!("pool acquire: {}", e))
84 + })?;
82 85
83 - /// Release a session-level PostgreSQL advisory lock.
84 - pub async fn advisory_unlock(pool: &PgPool, key: i64) -> Result<()> {
85 - sqlx::query("SELECT pg_advisory_unlock($1)")
86 - .bind(key)
87 - .execute(pool)
86 + // Lock, count, unlock — all on the same connection
87 + sqlx::query("SELECT pg_advisory_lock($1)")
88 + .bind(lock_key)
89 + .execute(&mut *conn)
88 90 .await?;
89 - Ok(())
91 +
92 + let count: i64 = sqlx::query_scalar(
93 + r#"
94 + SELECT COUNT(*) FROM users u
95 + JOIN user_sessions us ON us.user_id = u.id
96 + WHERE u.is_sandbox = TRUE
97 + AND u.sandbox_expires_at > NOW()
98 + AND us.ip_address = $1
99 + "#,
100 + )
101 + .bind(ip)
102 + .fetch_one(&mut *conn)
103 + .await?;
104 +
105 + sqlx::query("SELECT pg_advisory_unlock($1)")
106 + .bind(lock_key)
107 + .execute(&mut *conn)
108 + .await?;
109 +
110 + Ok(count)
90 111 }
M server/src/routes/pages/sandbox.rs +4 -10
@@ -58,14 +58,12 @@
58 58 AppError::BadRequest("Could not determine client address".to_string())
59 59 })?;
60 60
61 - // Enforce per-IP concurrent sandbox cap under an advisory lock to prevent
62 - // concurrent requests from both passing the count check before either inserts.
61 + // Enforce per-IP concurrent sandbox cap under an advisory lock.
62 + // Uses a single connection for lock + count + unlock to avoid the pool
63 + // connection mismatch bug with session-level advisory locks.
63 64 let lock_key = crate::helpers::ip_advisory_lock_key(&ip);
64 - db::advisory_lock(&state.db, lock_key).await?;
65 -
66 - let active = db::users::count_active_sandboxes_by_ip(&state.db, &ip).await?;
65 + let active = db::check_sandbox_cap(&state.db, lock_key, &ip).await?;
67 66 if active >= constants::SANDBOX_MAX_PER_IP {
68 - db::advisory_unlock(&state.db, lock_key).await?;
69 67 return Err(AppError::BadRequest(
70 68 "Too many active sandboxes from this address".to_string(),
71 69 ));
@@ -111,10 +109,6 @@
111 109 auth::login_user(&session, session_user).await?;
112 110 auth::track_session(&session, &state.db, user.id, &headers).await?;
113 111
114 - // Release the advisory lock now that the session row exists and the cap
115 - // query will see this sandbox account.
116 - db::advisory_unlock(&state.db, lock_key).await?;
117 -
118 112 // Session ends when the browser closes; the scheduler handles DB cleanup
119 113 session.set_expiry(Some(tower_sessions::Expiry::OnSessionEnd));
120 114