[release-branch.go1.9] database/sql: fix transaction leak
When the user context which passed in (*DB)BeginTx is canceled or
timeout, the current implementation could cause db transaction leak
in some extreme scenario.
Goroutine 1:
Call (*DB) BeginTx begins a transaction with a userContext.
In (*DB)BeginTx, a new goroutine (*Tx)awaitDone
which monitor context and rollback tx if needed will be created
Goroutine 2(awaitDone):
block on tx.ctx.Done()
Goroutine 1:
Execute some insert or update sqls on the database
Goroutine 1:
Commit the transaction, (*Tx)Commit set
the atomic variable tx.done to 1
Goroutine 3(maybe global timer):
Cancel userContext which be passed in Tx
Goroutine 1:
(*Tx)Commit checks tx.ctx.Done().
Due to the context has been canceled, it will return
context.Canceled or context.DeadlineExceeded error immediately
and abort the real COMMIT operation of transaction
Goroutine 2:
Release with tx.ctx.Done() signal, execute (*Tx)rollback.
However the atomic variable tx.done is 1 currently,
it will return ErrTxDone error immediately and
abort the real ROLLBACK operation of transaction
Fixes #22976
Change-Id: I3bc23adf25db823861d91e33d3cca6189fb1171d
Reviewed-on: https://go-review.googlesource.com/81736
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Reviewed-on: https://go-review.googlesource.com/88323
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>