database/sql: deadlock on transaction stmt context cancel [1.14 backport]

[gopherbot]

@pjm0616 requested issue #40985 to be considered for backport to the next 1.14 minor release.

@gopherbot @odeke-em Please consider this for backport to 1.15 and 1.14.
This regression, introduced in 1.14.6 and 1.15(by #34775), has a serious impact(deadlock) and no workarounds, other than patching Go manually.

[cagedmantis]

Approved as this is a serious issue without a known workaround.

[cagedmantis]

Please remember to create the cherry-pick CL.

[gopherbot]

Change https://golang.org/cl/284512 mentions this issue: [release-branch.go1.14] database/sql: fix tx stmt deadlock when rollback

[odeke-em]

Roger that, I've mailed a CL.

[cagedmantis]

Would @kardianos be willing to review this since they approved the original CL?

[dmitshur]

Closing because Go 1.16 is out, and there will not be a Go 1.14.16 minor release per release policy.