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runtime: "lock ordering problem" between fin and wbufSpans #41021

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bcmills opened this issue Aug 25, 2020 · 2 comments
Closed

runtime: "lock ordering problem" between fin and wbufSpans #41021

bcmills opened this issue Aug 25, 2020 · 2 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker
Milestone
Go1.16

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@bcmills
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bcmills commented Aug 25, 2020 •
edited

2020-08-24T21:08:46-95df156/linux-amd64-staticlockranking

##### ../misc/cgo/errors
--- FAIL: TestPointerChecks (1.07s)
    --- FAIL: TestPointerChecks/finalizer (0.04s)
        ptr_test.go:620: 111337  ======
            0 : fin 18 0x7dc400
            1 : wbufSpans 37 0x7aac70
            fatal error: lock ordering problem
            
            runtime stack:
            runtime.throw(0x4f7309, 0x15)
            	/workdir/go/src/runtime/panic.go:1116 +0x72
            runtime.checkRanks(0xc000082780, 0x12, 0x25)
            	/workdir/go/src/runtime/lockrank_on.go:141 +0x2a9
            runtime.lockWithRankMayAcquire.func1()
            	/workdir/go/src/runtime/lockrank_on.go:211 +0xac
            runtime.lockWithRankMayAcquire(0x7aac70, 0x25)
            	/workdir/go/src/runtime/lockrank_on.go:200 +0x6f
            runtime.getempty(0x7fd9e1a46e38)
            	/workdir/go/src/runtime/mgcwork.go:432 +0x4f
            runtime.(*gcWork).init(0xc000024e98)
            	/workdir/go/src/runtime/mgcwork.go:117 +0x25
            runtime.(*gcWork).putBatch(0xc000024e98, 0xc000024f58, 0x1, 0x200)
            	/workdir/go/src/runtime/mgcwork.go:245 +0x19f
            runtime.wbBufFlush1(0xc000023800)
            	/workdir/go/src/runtime/mwbbuf.go:315 +0x237
            runtime.wbBufFlush.func1()
            	/workdir/go/src/runtime/mwbbuf.go:218 +0x3a
            runtime.systemstack(0x0)
            	/workdir/go/src/runtime/asm_amd64.s:370 +0x66
            runtime.mstart()
            	/workdir/go/src/runtime/proc.go:1116
            
            goroutine 18 [running]:
            runtime.systemstack_switch()
            	/workdir/go/src/runtime/asm_amd64.s:330 fp=0xc00002a6a0 sp=0xc00002a698 pc=0x466ce0
            runtime.wbBufFlush(0x7a9eb8, 0xc000106300)
            	/workdir/go/src/runtime/mwbbuf.go:206 +0x66 fp=0xc00002a6d0 sp=0xc00002a6a0 pc=0x431b46
            runtime.gcWriteBarrier(0x7dc400, 0x12, 0xc00000c000, 0x2000000020, 0xc00002a7d0, 0x438c85, 0x20, 0x20, 0x20, 0x0, ...)
            	/workdir/go/src/runtime/asm_amd64.s:1461 +0xae fp=0xc00002a758 sp=0xc00002a6d0 pc=0x468b6e
            runtime.runfinq()
            	/workdir/go/src/runtime/mfinal.go:173 +0xd1 fp=0xc00002a7e0 sp=0xc00002a758 pc=0x41a771
            runtime.goexit()
            	/workdir/go/src/runtime/asm_amd64.s:1374 +0x1 fp=0xc00002a7e8 sp=0xc00002a7e0 pc=0x468aa1
            created by runtime.createfing
            	/workdir/go/src/runtime/mfinal.go:156 +0x65
            111337  ======
            0 : fin 18 0x7dc400
            1 : wbufSpans 37 0x7aac70
            2 : allg 11 0x7dc380
            fatal error: lock ordering problem
            panic during panic
            
            runtime stack:
            runtime.throw(0x4f7309, 0x15)
            	/workdir/go/src/runtime/panic.go:1116 +0x72
            runtime.checkRanks(0xc000082780, 0x25, 0xb)
            	/workdir/go/src/runtime/lockrank_on.go:141 +0x2a9
            runtime.lockWithRank.func1()
            	/workdir/go/src/runtime/lockrank_on.go:83 +0xbc
            runtime.lockWithRank(0x7dc380, 0xb)
            	/workdir/go/src/runtime/lockrank_on.go:72 +0x8e
            runtime.lock(...)
            	/workdir/go/src/runtime/lock_futex.go:47
            runtime.tracebackothers(0xc000082780)
            	/workdir/go/src/runtime/traceback.go:917 +0x93
            runtime.dopanic_m(0xc000082780, 0x436492, 0x7fd9e1a46cb0, 0x1)
            	/workdir/go/src/runtime/panic.go:1316 +0x2c9
            runtime.fatalthrow.func1()
            	/workdir/go/src/runtime/panic.go:1171 +0x5f
            runtime.fatalthrow()
            	/workdir/go/src/runtime/panic.go:1168 +0x57
            runtime.throw(0x4f7309, 0x15)
            	/workdir/go/src/runtime/panic.go:1116 +0x72
            runtime.checkRanks(0xc000082780, 0x12, 0x25)
            	/workdir/go/src/runtime/lockrank_on.go:141 +0x2a9
            runtime.lockWithRankMayAcquire.func1()
            	/workdir/go/src/runtime/lockrank_on.go:211 +0xac
            runtime.lockWithRankMayAcquire(0x7aac70, 0x25)
            	/workdir/go/src/runtime/lockrank_on.go:200 +0x6f
            runtime.getempty(0x7fd9e1a46e38)
            	/workdir/go/src/runtime/mgcwork.go:432 +0x4f
            runtime.(*gcWork).init(0xc000024e98)
            	/workdir/go/src/runtime/mgcwork.go:117 +0x25
            runtime.(*gcWork).putBatch(0xc000024e98, 0xc000024f58, 0x1, 0x200)
            	/workdir/go/src/runtime/mgcwork.go:245 +0x19f
            runtime.wbBufFlush1(0xc000023800)
            	/workdir/go/src/runtime/mwbbuf.go:315 +0x237
            runtime.wbBufFlush.func1()
            	/workdir/go/src/runtime/mwbbuf.go:218 +0x3a
            runtime.systemstack(0x0)
            	/workdir/go/src/runtime/asm_amd64.s:370 +0x66
            runtime.mstart()
            	/workdir/go/src/runtime/proc.go:1116
        ptr_test.go:621: failed unexpectedly with expensive checks: exit status 2
FAIL

CC @danscales @aclements @prattmic
@bcmills bcmills added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker labels Aug 25, 2020
@bcmills bcmills added this to the Go1.16 milestone Aug 25, 2020
@prattmic
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prattmic commented Aug 25, 2020 •
edited

This looks like a missing, but valid, edge on the wbufSpans lock. I'll send a CL.

IIUC, wbufSpans may be taken in any context that allows write barriers. As such, I'm a bit surprised to see its partial order list is not longer. The mheap list (locks held in contexts which may allocate) is significantly longer, but I'd expect contexts which may allocate and contexts which may have write barriers to be very similar.

This difference may just be because we've observed fewer of these edges since write barriers are only enabled during GC, while allocations can happen consistently.

@mknyszek do you see any extra locks that should obviously be added to wbufSpans? https://cs.opensource.google/go/go/+/master:src/runtime/lockrank.go;l=233-234

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Change https://golang.org/cl/250464 mentions this issue: runtime: add lock partial order edge (fin -> wbufSpans)

@golang golang locked and limited conversation to collaborators Aug 27, 2021
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