Issue 5191044: code review 5191044: runtime: fix spurious deadlock reporting

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Issue 5191044: code review 5191044: runtime: fix spurious deadlock reporting (Closed)

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Created:
13 years, 5 months ago by dvyukov

Modified:
13 years, 5 months ago

Reviewers:

CC:
golang-dev, rsc

Visibility:
Public.

Description

runtime: fix spurious deadlock reporting Fixes issue 2337. Unfortunate sequence of events is: 1. maxcpu=2, mcpu=1, grunning=1 2. starttheworld creates an extra M: maxcpu=2, mcpu=2, grunning=1 4. the goroutine calls runtime.GOMAXPROCS(1) maxcpu=1, mcpu=2, grunning=1 5. since it sees mcpu>maxcpu, it calls gosched() 6. schedule() deschedules the goroutine: maxcpu=1, mcpu=1, grunning=0 7. schedule() call getnextandunlock() which fails to pick up the goroutine again, because canaddcpu() fails, because mcpu==maxcpu 8. then it sees that grunning==0, reports deadlock and terminates

	Unified diffs	Side-by-side diffs	Delta from patch set	Stats (+34 lines, -11 lines)			Patch
M	src/pkg/runtime/malloc.h	View	1 2 3 4 5 6	1 chunk	+1 line, -1 line	0 comments	Download
M	src/pkg/runtime/mgc0.c	View	1 2 3 4 5 6	3 chunks	+3 lines, -3 lines	0 comments	Download
M	src/pkg/runtime/proc.c	View	1 2 3 4 5 6 7	4 chunks	+12 lines, -7 lines	0 comments	Download
A	test/fixedbugs/bug370.go	View	1 2 3 4	1 chunk	+18 lines, -0 lines	0 comments	Download

Messages

Total messages: 3

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dvyukov

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com), I'd like you to review this change to https://go.googlecode.com/hg/

13 years, 5 months ago (2011-10-06 15:05:31 UTC) #1

dvyukov

13 years, 5 months ago (2011-10-06 15:10:56 UTC) #3

*** Submitted as http://code.google.com/p/go/source/detail?r=09557b41f0ab ***

runtime: fix spurious deadlock reporting
Fixes issue 2337.
Unfortunate sequence of events is:
1. maxcpu=2, mcpu=1, grunning=1
2. starttheworld creates an extra M:
   maxcpu=2, mcpu=2, grunning=1
4. the goroutine calls runtime.GOMAXPROCS(1)
   maxcpu=1, mcpu=2, grunning=1
5. since it sees mcpu>maxcpu, it calls gosched()
6. schedule() deschedules the goroutine:
   maxcpu=1, mcpu=1, grunning=0
7. schedule() call getnextandunlock() which
   fails to pick up the goroutine again,
   because canaddcpu() fails, because mcpu==maxcpu
8. then it sees that grunning==0,
   reports deadlock and terminates

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/5191044

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