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database/sql: sync.Mutex unlocked when panic cause by context #54110

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fishery86 opened this issue Jul 28, 2022 · 5 comments
Closed

database/sql: sync.Mutex unlocked when panic cause by context #54110

fishery86 opened this issue Jul 28, 2022 · 5 comments
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@fishery86
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What version of Go are you using (go version)?

$ go1.17.2 darwin/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE=""
GOENV=""
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOOS="darwin"
GOPATH=""
GOROOT="/usr/local/Cellar/go/1.17.2/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.17.2/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.17.2"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

// with nil context.Context
tx, err := db.BeginTx(nil, nil)
if err != nil {
return err
}
defer tx.Commit()

goroutine 17183 [running]:
runtime/debug.Stack(0x1358240, 0xc0004e1aa0, 0x15129f9)
	/usr/local/go/src/runtime/debug/stack.go:24 +0x9f
....
panic(0x1342740, 0x1ef49d0)
	/usr/local/go/src/runtime/panic.go:965 +0x1b9
**************/context.(*MyContext).Done(0x0, 0xc000e6aae8)
	<autogenerated>:1 +0x2b
database/sql.(*DB).conn(0xc000367ad0, 0x16d2dc8, 0x0, 0x1, 0x13341c0, 0xc0004e1770, 0xc0006dc700)
	/usr/local/go/src/database/sql/sql.go:1205 +0xd7
database/sql.(*DB).begin(0xc000367ad0, 0x16d2dc8, 0x0, 0x0, 0xc000091b01, 0xc000091d40, 0xfa3e0b, 0xc0004baa50)
	/usr/local/go/src/database/sql/sql.go:1752 +0x4f
database/sql.(*DB).BeginTx(0xc000367ad0, 0x16d2dc8, 0x0, 0x0, 0xc000367ad0, 0x1, 0xc000e6abd0)
	/usr/local/go/src/database/sql/sql.go:1734 +0x8f

panic happend in conn and it makes locker not be unlocked

// conn returns a newly-opened or cached *driverConn.
func (db *DB) conn(ctx context.Context, strategy connReuseStrategy) (*driverConn, error) {
	db.mu.Lock()
	if db.closed {
		db.mu.Unlock()
		return nil, errDBClosed
	}
	// Check if the context is expired.
	select {
	default:
	case <-ctx.Done(): // panic here and db.mu will not be unlocked ,it causes conns hang-up
		db.mu.Unlock()
		return nil, ctx.Err()
	}
	lifetime := db.maxLifetime
    // .....
}




### What did you expect to see?

db.mu.Unlock() should be called
@andig
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andig commented Jul 28, 2022 •
edited

Why or how should ctx.Done() panic? Are you sure that's what is happening?

@fishery86
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ctx.Done() should not panic normally,but it may panic unexpected. And ctx may unexpectly be nil, it makes the same result.

@fishery86 fishery86 mentioned this issue Jul 28, 2022
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@ianlancetaylor
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Don't pass a nil context. Go code doesn't try to handle every conceivable panic. This program has a logic error which should be caught by ordinary testing, and there is no need for the standard library to handle this case. Sorry.

@ianlancetaylor ianlancetaylor closed this as not planned Won't fix, can't repro, duplicate, stale Jul 28, 2022
@fishery86
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fishery86 commented Jul 29, 2022 •
edited

Don't pass a nil context. Go code doesn't try to handle every conceivable panic. This program has a logic error which should be caught by ordinary testing, and there is no need for the standard library to handle this case. Sorry.

quite agree that. and I think the code now could be fixed to avoid hang-up when panic happened. As the PR #54144 does,it does not handle the panic caused by context ,but it avoid locker be unlocked,and make it running on right way.

@gopherbot
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Change https://go.dev/cl/420074 mentions this issue: database/sql: check context expire before lock

@golang golang locked and limited conversation to collaborators Jul 29, 2023
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database/sql: check context expire before lock fishery86/go
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@andig @ianlancetaylor @gopherbot @fishery86