database/sql: segmentation violation

[kardianos]

from builder log: https://build.golang.org/log/2c3b36d6c05318edc47728998463214689d2f2e2

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x30 pc=0x56ecd6]

goroutine 318 [running]:
database/sql.ctxDriverPrepare(0x6f3300, 0xc420202720, 0x0, 0x0, 0xc4201f86e0, 0x1d, 0x0, 0x0, 0x0, 0x0)
	/tmp/workdir/go/src/database/sql/ctxutil.go:17 +0x1c6
database/sql.(*DB).queryConn.func2()
	/tmp/workdir/go/src/database/sql/sql.go:1263 +0xb9
database/sql.withLock(0x6f2000, 0xc4200facb0, 0xc4203b7d98)
	/tmp/workdir/go/src/database/sql/sql.go:2441 +0x67
database/sql.(*DB).queryConn(0xc42023d970, 0x6f3300, 0xc420202720, 0xc4200facb0, 0x639fb0, 0xc4201f86e0, 0x1d, 0x0, 0x0, 0x0, ...)
	/tmp/workdir/go/src/database/sql/sql.go:1264 +0x683
database/sql.(*Tx).QueryContext(0xc4202027e0, 0x6f3300, 0xc420202720, 0xc4201f86e0, 0x1d, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/tmp/workdir/go/src/database/sql/sql.go:1669 +0x176
database/sql.TestIssue18429.func1(0xc420386e80, 0xc420394b30, 0x6f32c0, 0xc42009ad68, 0xc42023d970)
	/tmp/workdir/go/src/database/sql/sql_test.go:2645 +0x253
created by database/sql.TestIssue18429
	/tmp/workdir/go/src/database/sql/sql_test.go:2652 +0x1c9
FAIL	database/sql	0.160s

Is this a runtime issue or is the driver.Conn actually nil?

[bradfitz]

@kardianos, anything suspicious or racy in the test?

Otherwise, cc @aclements @randall77 @cherrymui.

[kardianos]

TestIssue18429 was designed to test the race condition in Tx.rollback. I don't think there is anything suspicious in the test itself.

After looking at this for a bit, I think this may be an issue with database/sql, not runtime. If driverConn.finalClose is called while DB.queryConn is running this may happen. We are correctly guarding data changes with a mutex, but not checking for a nil dc.ci in that lock. This is probably possible after any time currently if a context is canceled. I'll look into this further.

[kardianos]

I'm able to reproduce this issue on my box with a modified TestIssue18429 function. Not a runtime issue.

[kardianos]

I'm not sure why gobot didn't post it, but this should be resolved with https://go-review.googlesource.com/c/35550/

[gopherbot]

CL https://golang.org/cl/35550 mentions this issue.