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Fix race condition in query cancellation #578

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merged 1 commit into from
Mar 13, 2017
Merged

Fix race condition in query cancellation #578

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32 changes: 14 additions & 18 deletions conn.go
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Original file line number Diff line number Diff line change
Expand Up @@ -98,7 +98,7 @@ type conn struct {
namei int
scratch [512]byte
txnStatus transactionStatus
txnClosed chan<- struct{}
txnFinish func()

// Save connection arguments to use during CancelRequest.
dialer Dialer
Expand Down Expand Up @@ -528,9 +528,8 @@ func (cn *conn) Begin() (_ driver.Tx, err error) {
}

func (cn *conn) closeTxn() {
if cn.txnClosed != nil {
close(cn.txnClosed)
cn.txnClosed = nil
if finish := cn.txnFinish; finish != nil {
finish()
}
}

Expand Down Expand Up @@ -893,16 +892,9 @@ func (cn *conn) send(m *writeBuf) {
}
}

func (cn *conn) sendStartupPacket(m *writeBuf) {
// sanity check
if m.buf[0] != 0 {
panic("oops")
}

func (cn *conn) sendStartupPacket(m *writeBuf) error {
_, err := cn.c.Write((m.wrap())[1:])
if err != nil {
panic(err)
}
return err
}

// Send a message of type typ to the server on the other end of cn. The
Expand Down Expand Up @@ -1024,7 +1016,9 @@ func (cn *conn) ssl(o values) {

w := cn.writeBuf(0)
w.int32(80877103)
cn.sendStartupPacket(w)
if err := cn.sendStartupPacket(w); err != nil {
panic(err)
}

b := cn.scratch[:1]
_, err := io.ReadFull(cn.c, b)
Expand Down Expand Up @@ -1085,7 +1079,9 @@ func (cn *conn) startup(o values) {
w.string(v)
}
w.string("")
cn.sendStartupPacket(w)
if err := cn.sendStartupPacket(w); err != nil {
panic(err)
}

for {
t, r := cn.recv()
Expand Down Expand Up @@ -1319,7 +1315,7 @@ func (cn *conn) parseComplete(commandTag string) (driver.Result, string) {

type rows struct {
cn *conn
closed chan<- struct{}
finish func()
colNames []string
colTyps []oid.Oid
colFmts []format
Expand All @@ -1330,8 +1326,8 @@ type rows struct {
}

func (rs *rows) Close() error {
if rs.closed != nil {
defer close(rs.closed)
if finish := rs.finish; finish != nil {
defer finish()
}
// no need to look at cn.bad as Next() will
for {
Expand Down
64 changes: 41 additions & 23 deletions conn_go18.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@ import (
"context"
"database/sql/driver"
"errors"
"io"
"io/ioutil"
)

// Implement the "QueryerContext" interface
Expand All @@ -14,12 +16,12 @@ func (cn *conn) QueryContext(ctx context.Context, query string, args []driver.Na
for i, nv := range args {
list[i] = nv.Value
}
closed := cn.watchCancel(ctx)
finish := cn.watchCancel(ctx)
r, err := cn.query(query, list)
if err != nil {
return nil, err
}
r.closed = closed
r.finish = finish
return r, nil
}

Expand All @@ -30,8 +32,8 @@ func (cn *conn) ExecContext(ctx context.Context, query string, args []driver.Nam
list[i] = nv.Value
}

if closed := cn.watchCancel(ctx); closed != nil {
defer close(closed)
if finish := cn.watchCancel(ctx); finish != nil {
defer finish()
}

return cn.Exec(query, list)
Expand All @@ -49,41 +51,57 @@ func (cn *conn) BeginTx(ctx context.Context, opts driver.TxOptions) (driver.Tx,
if err != nil {
return nil, err
}
cn.txnClosed = cn.watchCancel(ctx)
cn.txnFinish = cn.watchCancel(ctx)
return tx, nil
}

func (cn *conn) watchCancel(ctx context.Context) chan<- struct{} {
func (cn *conn) watchCancel(ctx context.Context) func() {
if done := ctx.Done(); done != nil {
closed := make(chan struct{})
finished := make(chan struct{})
go func() {
select {
case <-done:
cn.cancel()
case <-closed:
_ = cn.cancel()
finished <- struct{}{}
case <-finished:
}
}()
return closed
return func() {
select {
case <-finished:
case finished <- struct{}{}:
}
}
}
return nil
}

func (cn *conn) cancel() {
var err error
can := &conn{}
can.c, err = dial(cn.dialer, cn.opts)
func (cn *conn) cancel() error {
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Why are we returning errors here at all? They are never used. In case we want them in the future and it's just good practice?

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Yes, that was my thinking.

c, err := dial(cn.dialer, cn.opts)
if err != nil {
return
return err
}
can.ssl(cn.opts)
defer c.Close()

defer can.errRecover(&err)
{
can := conn{
c: c,
}
can.ssl(cn.opts)

w := can.writeBuf(0)
w.int32(80877102) // cancel request code
w.int32(cn.processID)
w.int32(cn.secretKey)
w := can.writeBuf(0)
w.int32(80877102) // cancel request code
w.int32(cn.processID)
w.int32(cn.secretKey)

can.sendStartupPacket(w)
_ = can.c.Close()
if err := can.sendStartupPacket(w); err != nil {
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I don't see how the panics are caught here. cancel() is only invoked in a go routine, which means a defer'd recover in another go routine won't see it.

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sendStartupPacket no longer panics, though.

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Ah, I didn't see that change cuz no reviewable.

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Yeah, GH reviews are terrible. Pro tip though: you can just navigate to https://reviewable.io/reviews/lib/pq/578.

return err
}
}

// Read until EOF to ensure that the server received the cancel.
{
_, err := io.Copy(ioutil.Discard, c)
return err
}
}
54 changes: 54 additions & 0 deletions go18_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -72,6 +72,8 @@ func TestMultipleSimpleQuery(t *testing.T) {
}
}

const contextRaceIterations = 100

func TestContextCancelExec(t *testing.T) {
db := openTestConn(t)
defer db.Close()
Expand All @@ -94,6 +96,20 @@ func TestContextCancelExec(t *testing.T) {
} else if err.Error() != "context canceled" {
t.Fatalf("unexpected error: %s", err)
}

for i := 0; i < contextRaceIterations; i++ {
func() {
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
if _, err := db.ExecContext(ctx, "select 1"); err != nil {
t.Fatal(err)
}
}()

if _, err := db.Exec("select 1"); err != nil {
t.Fatal(err)
}
}
}

func TestContextCancelQuery(t *testing.T) {
Expand All @@ -118,6 +134,25 @@ func TestContextCancelQuery(t *testing.T) {
} else if err.Error() != "context canceled" {
t.Fatalf("unexpected error: %s", err)
}

for i := 0; i < contextRaceIterations; i++ {
func() {
ctx, cancel := context.WithCancel(context.Background())
rows, err := db.QueryContext(ctx, "select 1")
cancel()
if err != nil {
t.Fatal(err)
} else if err := rows.Close(); err != nil {
t.Fatal(err)
}
}()

if rows, err := db.Query("select 1"); err != nil {
t.Fatal(err)
} else if err := rows.Close(); err != nil {
t.Fatal(err)
}
}
}

func TestContextCancelBegin(t *testing.T) {
Expand Down Expand Up @@ -153,4 +188,23 @@ func TestContextCancelBegin(t *testing.T) {
} else if err.Error() != "context canceled" {
t.Fatalf("unexpected error: %s", err)
}

for i := 0; i < contextRaceIterations; i++ {
func() {
ctx, cancel := context.WithCancel(context.Background())
tx, err := db.BeginTx(ctx, nil)
cancel()
if err != nil {
t.Fatal(err)
} else if err := tx.Rollback(); err != nil && err != sql.ErrTxDone {
t.Fatal(err)
}
}()

if tx, err := db.Begin(); err != nil {
t.Fatal(err)
} else if err := tx.Rollback(); err != nil {
t.Fatal(err)
}
}
}