Validation Functions can not call vars.GlobalVarsAccessor.GetGlobalSysVar safely

[morgo]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Start a tidb server with the following config:

[performance]
feedback-probability = 0.05

Because of #29594 it will cause the server to crash within a few seconds:

[2021/11/29 21:21:24.783 -07:00] [WARN] [memory_usage_alarm.go:140] ["tidb-server has the risk of OOM. Running SQLs and heap profile will be recorded in record path"] ["is server-memory-quota set"=false] ["system memory total"=67354476544] ["system memory usage"=54284972032] ["tidb-server memory usage"=283271120] [memory-usage-alarm-ratio=0.8] ["record path"="/tmp/1002_tidb/MC4wLjAuMDo0MDAwLzAuMC4wLjA6MTAwODA=/tmp-storage/record"]
runtime: goroutine stack exceeds 1000000000-byte limit
runtime: sp=0xc031c0a380 stack=[0xc031c0a000, 0xc051c0a000]
fatal error: stack overflow

runtime stack:
runtime.throw(0x3db7367, 0xe)
	/usr/local/go/src/runtime/panic.go:1117 +0x72
runtime.newstack()
	/usr/local/go/src/runtime/stack.go:1069 +0x7ed
runtime.morestack()
	/usr/local/go/src/runtime/asm_amd64.s:458 +0x8f

goroutine 809 [running]:
runtime.mapaccess1(0x39155e0, 0xc0115e6390, 0xc031c0a3c0, 0x0)
	/usr/local/go/src/runtime/map.go:394 +0x24d fp=0xc031c0a390 sp=0xc031c0a388 pc=0x129ed2d
github.com/pingcap/tidb/session.(*session).Value(0xc010754c00, 0x42addc0, 0x3ec0d50, 0x0, 0x0)
	/home/morgo/go/src/github.com/morgo/tidb/session/session.go:2165 +0x77 fp=0xc031c0a3e0 sp=0xc031c0a390 pc=0x341e557
github.com/pingcap/tidb/session.(*session).GetGlobalSysVar(0xc010754c00, 0x3dcc2cf, 0x14, 0xc011828c37, 0x1, 0xc01162e000, 0xc011828c37)
	/home/morgo/go/src/github.com/morgo/tidb/session/session.go:1092 +0x5b fp=0xc031c0a590 sp=0xc031c0a3e0 pc=0x341325b
github.com/pingcap/tidb/sessionctx/variable.glob..func250(0xc01162e000, 0xc011828c37, 0x1, 0xc011828c37, 0x1, 0xc011828c01, 0x1, 0x0, 0x0, 0xc0115e6390)
	/home/morgo/go/src/github.com/morgo/tidb/sessionctx/variable/sysvar.go:1721 +0xa9 fp=0xc031c0a5f0 sp=0xc031c0a590 pc=0x2123869
github.com/pingcap/tidb/sessionctx/variable.(*SysVar).ValidateWithRelaxedValidation(0x58aff60, 0xc01162e000, 0xc011828c37, 0x1, 0x1, 0x0, 0x0)
	/home/morgo/go/src/github.com/morgo/tidb/sessionctx/variable/sysvar.go:339 +0x19e fp=0xc031c0a680 sp=0xc031c0a5f0 pc=0x211225e
github.com/pingcap/tidb/session.(*session).GetGlobalSysVar(0xc010754c00, 0x3dcc2cf, 0x14, 0xc011828c37, 0x1, 0xc01162e000, 0xc011828c37)
	/home/morgo/go/src/github.com/morgo/tidb/session/session.go:1121 +0x5e5 fp=0xc031c0a830 sp=0xc031c0a680 pc=0x34137e5
github.com/pingcap/tidb/sessionctx/variable.glob..func250(0xc01162e000, 0xc011828c37, 0x1, 0xc011828c37, 0x1, 0xc011828c01, 0x1, 0x0, 0x0, 0xc0115e6390)
	/home/morgo/go/src/github.com/morgo/tidb/sessionctx/variable/sysvar.go:1721 +0xa9 fp=0xc031c0a890 sp=0xc031c0a830 pc=0x2123869
..

The root cause is because the validation function on TiDBAnalyzeVersion calls vars.GlobalVarsAccessor.GetGlobalSysVar(TiDBAnalyzeVersion), which causes recursion, because the GetGlobalSysVar() func will in turn call the validation function.

There are 3 other occurences of vars.GlobalVarsAccessor.GetGlobalSysVar being used in a validation function, but these don't lead to recursion. It is only this instance.

2. What did you expect to see? (Required)

No crash

3. What did you see instead (Required)

Crash

4. What is your TiDB version? (Required)

master

[aytrack]

releated to #27166

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.

[Lily2025]

/severity Critical