runtime: cannot allocate memory on Plan 9

[0intro]

The runtime/pprof trace_parser_test.go and trace_test.go
test files were added in CL 2039.

These new tests were failing and emphasized an issue
in the memory allocator on Plan 9 that could lead
to a corruption (issue #9712).

Dmitry Vyukov (@dvyukov) kindly fixed the memory allocator
on Plan 9 in CL 3602.

However, the TestTrace test is still randomly failing.

For example:

http://build.golang.org/log/f3be10946ca4bd08b55b6fb0e4169f10058a059c

fatal error: runtime: cannot allocate memory

runtime stack:
runtime.throw(0x1a68a8, 0x1f)
    /tmp/buildlet-scatch183758248/go/src/runtime/panic.go:511 +0x71
runtime.persistentalloc(0x4000, 0x8, 0x276f98, 0x19eaa)
    /tmp/buildlet-scatch183758248/go/src/runtime/malloc.go:634 +0x1ec
runtime.fixAlloc_Alloc(0x267d40, 0x0)
    /tmp/buildlet-scatch183758248/go/src/runtime/mfixalloc.go:39 +0xc8
runtime.mHeap_AllocSpanLocked(0x260e40, 0x1, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mheap.go:308 +0x155
runtime.mHeap_Alloc_m(0x260e40, 0x1, 0x6, 0xb400, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mheap.go:193 +0x125
runtime.func·034()
    /tmp/buildlet-scatch183758248/go/src/runtime/mheap.go:233 +0x51
runtime.systemstack(0xdfffec5c)
    /tmp/buildlet-scatch183758248/go/src/runtime/asm_386.s:270 +0x7f
runtime.mHeap_Alloc(0x260e40, 0x1, 0x6, 0x100, 0xb267)
    /tmp/buildlet-scatch183758248/go/src/runtime/mheap.go:234 +0x5f
runtime.mCentral_Grow(0x264f80, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mcentral.go:179 +0x89
runtime.mCentral_CacheSpan(0x264f80, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mcentral.go:75 +0x2e4
runtime.mCache_Refill(0x30384000, 0x6, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mcache.go:70 +0xa6
runtime.func·003()
    /tmp/buildlet-scatch183758248/go/src/runtime/malloc.go:161 +0x39
runtime.systemstack(0x1039c000)
    /tmp/buildlet-scatch183758248/go/src/runtime/asm_386.s:254 +0x56
runtime.mstart()
    /tmp/buildlet-scatch183758248/go/src/runtime/proc1.go:671

goroutine 50 [running]:
runtime.systemstack_switch()
    /tmp/buildlet-scatch183758248/go/src/runtime/asm_386.s:209 fp=0x1039fc98 sp=0x1039fc94
runtime.mallocgc(0x50, 0x16e6c0, 0x0, 0x1787df90)
    /tmp/buildlet-scatch183758248/go/src/runtime/malloc.go:162 +0x45c fp=0x1039fcf4 sp=0x1039fc98
runtime.newobject(0x16e6c0, 0x1787df90)
    /tmp/buildlet-scatch183758248/go/src/runtime/malloc.go:259 +0x47 fp=0x1039fd08 sp=0x1039fcf4
runtime/pprof_test.parseEvents(0x18d5e000, 0x52b7b, 0x58ccc, 0x177e4000, 0x186da, 0x1e000, 0x0, 0x0)
    /tmp/buildlet-scatch183758248/go/src/runtime/pprof/trace_parser_test.go:212 +0xa6d fp=0x1039fe98 sp=0x1039fd08
runtime/pprof_test.parseTrace(0x303a6f20, 0x103f5e60, 0x0, 0x0, 0x0, 0x0, 0x0)
    /tmp/buildlet-scatch183758248/go/src/runtime/pprof/trace_parser_test.go:63 +0xb8 fp=0x1039fedc sp=0x1039fe98
runtime/pprof_test.TestTraceStress(0x103f5e00)
    /tmp/buildlet-scatch183758248/go/src/runtime/pprof/trace_test.go:201 +0xb24 fp=0x1039ffb4 sp=0x1039fedc
testing.tRunner(0x103f5e00, 0x25a338)
    /tmp/buildlet-scatch183758248/go/src/testing/testing.go:448 +0xb4 fp=0x1039ffe8 sp=0x1039ffb4
runtime.goexit()
    /tmp/buildlet-scatch183758248/go/src/runtime/asm_386.s:2414 +0x1 fp=0x1039ffec sp=0x1039ffe8
created by testing.RunTests
    /tmp/buildlet-scatch183758248/go/src/testing/testing.go:556 +0x833

goroutine 1 [chan receive]:
testing.RunTests(0x1d12d8, 0x25a2c0, 0xc, 0xc, 0x1)
    /tmp/buildlet-scatch183758248/go/src/testing/testing.go:557 +0x86b
testing.(*M).Run(0x103d4060, 0x270060)
    /tmp/buildlet-scatch183758248/go/src/testing/testing.go:486 +0x5d
main.main()
    runtime/pprof/_test/_testmain.go:76 +0x176

goroutine 82 [select (no cases)]:
runtime/pprof_test.func·025()
    /tmp/buildlet-scatch183758248/go/src/runtime/pprof/trace_test.go:189 +0x22
created by runtime/pprof_test.TestTraceStress
    /tmp/buildlet-scatch183758248/go/src/runtime/pprof/trace_test.go:190 +0xa13
fatal error: malloc deadlock
panic during panic

runtime stack:
runtime.startpanic_m()
    /tmp/buildlet-scatch183758248/go/src/runtime/panic1.go:66 +0x11b
runtime.systemstack(0x1d14ec)
    /tmp/buildlet-scatch183758248/go/src/runtime/asm_386.s:270 +0x7f
runtime.startpanic()
    /tmp/buildlet-scatch183758248/go/src/runtime/panic.go:489 +0x10
runtime.throw(0x18fd18, 0xf)
    /tmp/buildlet-scatch183758248/go/src/runtime/panic.go:510 +0x65
runtime.mallocgc(0x8, 0x0, 0x3, 0xbe)
    /tmp/buildlet-scatch183758248/go/src/runtime/malloc.go:69 +0x8d
runtime.rawbyteslice(0x1, 0x0, 0x0, 0x0)
    /tmp/buildlet-scatch183758248/go/src/runtime/string.go:274 +0x77
runtime.stringtoslicebyte(0xdfffeb16, 0x1, 0x0, 0x0, 0x0)
    /tmp/buildlet-scatch183758248/go/src/runtime/string.go:133 +0x3f
runtime.exit(0x2)
    /tmp/buildlet-scatch183758248/go/src/runtime/os1_plan9.go:185 +0x109
runtime.dopanic_m(0x10382e60, 0x1ffb1, 0xdfffebb0)
    /tmp/buildlet-scatch183758248/go/src/runtime/panic1.go:121 +0x21b
runtime.func·043()
    /tmp/buildlet-scatch183758248/go/src/runtime/panic.go:498 +0x3e
runtime.systemstack(0xdfffeb9c)
    /tmp/buildlet-scatch183758248/go/src/runtime/asm_386.s:270 +0x7f
runtime.dopanic(0x0)
    /tmp/buildlet-scatch183758248/go/src/runtime/panic.go:499 +0x56
runtime.throw(0x1a68a8, 0x1f)
    /tmp/buildlet-scatch183758248/go/src/runtime/panic.go:511 +0x71
runtime.persistentalloc(0x4000, 0x8, 0x276f98, 0x19eaa)
    /tmp/buildlet-scatch183758248/go/src/runtime/malloc.go:634 +0x1ec
runtime.fixAlloc_Alloc(0x267d40, 0x0)
    /tmp/buildlet-scatch183758248/go/src/runtime/mfixalloc.go:39 +0xc8
runtime.mHeap_AllocSpanLocked(0x260e40, 0x1, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mheap.go:308 +0x155
runtime.mHeap_Alloc_m(0x260e40, 0x1, 0x6, 0xb400, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mheap.go:193 +0x125
runtime.func·034()
    /tmp/buildlet-scatch183758248/go/src/runtime/mheap.go:233 +0x51
runtime.systemstack(0xdfffec5c)
    /tmp/buildlet-scatch183758248/go/src/runtime/asm_386.s:270 +0x7f
runtime.mHeap_Alloc(0x260e40, 0x1, 0x6, 0x100, 0xb267)
    /tmp/buildlet-scatch183758248/go/src/runtime/mheap.go:234 +0x5f
runtime.mCentral_Grow(0x264f80, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mcentral.go:179 +0x89
runtime.mCentral_CacheSpan(0x264f80, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mcentral.go:75 +0x2e4
runtime.mCache_Refill(0x30384000, 0x6, 0x303c085c)
    /tmp/buildlet-scatch183758248/go/src/runtime/mcache.go:70 +0xa6
runtime.func·003()
    /tmp/buildlet-scatch183758248/go/src/runtime/malloc.go:161 +0x39
runtime.systemstack(0x1039c000)
    /tmp/buildlet-scatch183758248/go/src/runtime/asm_386.s:254 +0x56
runtime.mstart()
    /tmp/buildlet-scatch183758248/go/src/runtime/proc1.go:671
fatal error: unexpected signal during runtime execution
stack trace unavailable
fatal error: malloc deadlock
[...]
fatal error: malloc deadlock
pprof.test 2266: suicide: sys: breakpoint pc=0x00040567
*** Test killed: ran too long (5m0s).
FAIL    runtime/pprof   300.052s

[dvyukov]

This can be due to #9736