From c77418f4cac41c42566ca90921a1f928995cfba2 Mon Sep 17 00:00:00 2001 From: Emmanuel T Odeke Date: Mon, 18 Jan 2021 16:18:11 -0800 Subject: [release-branch.go1.15] database/sql: fix tx stmt deadlock when rollback Tx acquires tx.closemu W-lock and then acquires stmt.closemu.W-lock to fully close the transaction and associated prepared statement. Stmt query and execution run in reverse ways - acquires stmt.closemu.R-lock and then acquires tx.closemu.R-lock to grab tx connection, which may cause deadlock. Prevent the lock is held around tx.closePrepared to ensure no deadlock happens. Includes a test fix from CL 266097. Fixes #42884 Updates #40985 Updates #42259 Change-Id: Id52737660ada3cebdfff6efc23366cdc3224b8e8 Reviewed-on: https://go-review.googlesource.com/c/go/+/250178 Run-TryBot: Emmanuel Odeke TryBot-Result: Go Bot Reviewed-by: Daniel Theophanes Trust: Emmanuel Odeke (cherry picked from commit d4c1ad882973e407ff85b977f4ce5b9435451190) Reviewed-on: https://go-review.googlesource.com/c/go/+/284513 Reviewed-by: Dmitri Shuralyov --- src/database/sql/sql.go | 14 +++++++------- src/database/sql/sql_test.go | 28 ++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+), 7 deletions(-) diff --git a/src/database/sql/sql.go b/src/database/sql/sql.go index b3d0653f5c..3d1367d28f 100644 --- a/src/database/sql/sql.go +++ b/src/database/sql/sql.go @@ -2080,10 +2080,10 @@ func (tx *Tx) isDone() bool { // that has already been committed or rolled back. var ErrTxDone = errors.New("sql: transaction has already been committed or rolled back") -// closeLocked returns the connection to the pool and +// close returns the connection to the pool and // must only be called by Tx.rollback or Tx.Commit while -// closemu is Locked and tx already canceled. -func (tx *Tx) closeLocked(err error) { +// tx is already canceled and won't be executed concurrently. +func (tx *Tx) close(err error) { tx.releaseConn(err) tx.dc = nil tx.txi = nil @@ -2157,7 +2157,7 @@ func (tx *Tx) Commit() error { // to ensure no other connection has an active query. tx.cancel() tx.closemu.Lock() - defer tx.closemu.Unlock() + tx.closemu.Unlock() var err error withLock(tx.dc, func() { @@ -2166,7 +2166,7 @@ func (tx *Tx) Commit() error { if err != driver.ErrBadConn { tx.closePrepared() } - tx.closeLocked(err) + tx.close(err) return err } @@ -2189,7 +2189,7 @@ func (tx *Tx) rollback(discardConn bool) error { // to ensure no other connection has an active query. tx.cancel() tx.closemu.Lock() - defer tx.closemu.Unlock() + tx.closemu.Unlock() var err error withLock(tx.dc, func() { @@ -2201,7 +2201,7 @@ func (tx *Tx) rollback(discardConn bool) error { if discardConn { err = driver.ErrBadConn } - tx.closeLocked(err) + tx.close(err) return err } diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go index 5727f0d8aa..d7d4642608 100644 --- a/src/database/sql/sql_test.go +++ b/src/database/sql/sql_test.go @@ -2810,6 +2810,34 @@ func TestTxCannotCommitAfterRollback(t *testing.T) { } } +// Issue 40985 transaction statement deadlock while context cancel. +func TestTxStmtDeadlock(t *testing.T) { + db := newTestDB(t, "people") + defer closeDB(t, db) + + ctx, cancel := context.WithTimeout(context.Background(), 5*time.Millisecond) + defer cancel() + tx, err := db.BeginTx(ctx, nil) + if err != nil { + t.Fatal(err) + } + + stmt, err := tx.Prepare("SELECT|people|name,age|age=?") + if err != nil { + t.Fatal(err) + } + // Run number of stmt queries to reproduce deadlock from context cancel + for i := 0; i < 1e3; i++ { + // Encounter any close related errors (e.g.. ErrTxDone, stmt is closed) + // is expected due to context cancel. + _, err = stmt.Query(1) + if err != nil { + break + } + } + _ = tx.Rollback() +} + // Issue32530 encounters an issue where a connection may // expire right after it comes out of a used connection pool // even when a new connection is requested. -- cgit v1.2.3-54-g00ecf