Skip to content

G
golang
Switch branch/tag
  1. 01 Dec, 2014 2 commits
    • Russ Cox's avatar
      runtime: fix hang in GC due to shrinkstack vs netpoll race · 2b62e1ea
      Russ Cox authored 
      During garbage collection, after scanning a stack, we think about
shrinking it to reclaim some memory. The shrinking code (called
while the world is stopped) checked that the status was Gwaiting
or Grunnable and then changed the state to Gcopystack, to essentially
lock the stack so that no other GC thread is scanning it.
The same locking happens for stack growth (and is more necessary there).

        oldstatus = runtime·readgstatus(gp);
        oldstatus &= ~Gscan;
        if(oldstatus == Gwaiting || oldstatus == Grunnable)
                runtime·casgstatus(gp, oldstatus, Gcopystack); // oldstatus is Gwaiting or Grunnable
        else
                runtime·throw("copystack: bad status, not Gwaiting or Grunnable");

Unfortunately, "stop the world" doesn't stop everything. It stops all
normal goroutine execution, but the network polling thread is still
blocked in epoll and may wake up. If it does, and it chooses a goroutine
to mark runnable, and that goroutine is the one whose stack is shrinking,
then it can happen that between readgstatus and casgstatus, the status
changes from Gwaiting to Grunnable.

casgstatus assumes that if the status is not what is expected, it is a
transient change (like from Gwaiting to Gscanwaiting and back, or like
from Gwaiting to Gcopystack and back), and it loops until the status
has been restored to the expected value. In this case, the status has
changed semi-permanently from Gwaiting to Grunnable - it won't
change again until the GC is done and the world can continue, but the
GC is waiting for the status to change back. This wedges the program.

To fix, call a special variant of casgstatus that accepts either Gwaiting
or Grunnable as valid statuses.

Without the fix bug with the extra check+throw in casgstatus, the
program below dies in a few seconds (2-10) with GOMAXPROCS=8
on a 2012 Retina MacBook Pro. With the fix, it runs for minutes
and minutes.

package main

import (
        "io"
        "log"
        "net"
        "runtime"
)

func main() {
        const N = 100
        for i := 0; i < N; i++ {
                l, err := net.Listen("tcp", "127.0.0.1:0")
                if err != nil {
                        log.Fatal(err)
                }
                ch := make(chan net.Conn, 1)
                go func() {
                        var err error
                        c1, err := net.Dial("tcp", l.Addr().String())
                        if err != nil {
                                log.Fatal(err)
                        }
                        ch <- c1
                }()
                c2, err := l.Accept()
                if err != nil {
                        log.Fatal(err)
                }
                c1 := <-ch
                l.Close()
                go netguy(c1, c2)
                go netguy(c2, c1)
                c1.Write(make([]byte, 100))
        }
        for {
                runtime.GC()
        }
}

func netguy(r, w net.Conn) {
        buf := make([]byte, 100)
        for {
                bigstack(1000)
                _, err := io.ReadFull(r, buf)
                if err != nil {
                        log.Fatal(err)
                }
                w.Write(buf)
        }
}

var g int

func bigstack(n int) {
        var buf [100]byte
        if n > 0 {
                bigstack(n - 1)
        }
        g = int(buf[0]) + int(buf[99])
}

Fixes #9186.

LGTM=rlh
R=austin, rlh
CC=dvyukov, golang-codereviews, iant, khr, r
https://golang.org/cl/179680043
      2b62e1ea
    • Keith Randall's avatar
      reflect: Fix reflect.funcLayout. The GC bitmap has two bits per · 7c1e3303
      Keith Randall authored 
      pointer, not one.

Fixes #9179

LGTM=iant, rsc
R=golang-codereviews, iant, rsc
CC=golang-codereviews
https://golang.org/cl/182160043
      7c1e3303
  3. 25 Nov, 2014 2 commits
  5. 22 Nov, 2014 2 commits
  7. 20 Nov, 2014 3 commits
  9. 19 Nov, 2014 2 commits
    • Russ Cox's avatar
      runtime: remove assumption that noptrdata data bss noptrbss are ordered and contiguous · 378c2515
      Russ Cox authored 
      The assumption can be violated by external linkers reordering them or
inserting non-Go sections in between them. I looked briefly at trying
to write out the _go_.o in external linking mode in a way that forced
the ordering, but no matter what there's no way to force Go's data
and Go's bss to be next to each other. If there is any data or bss from
non-Go objects, it's very likely to get stuck in between them.

Instead, rewrite the two places we know about that make the assumption.
I grepped for noptrdata to look for more and didn't find any.

The added race test (os/exec in external linking mode) fails without
the changes in the runtime. It crashes with an invalid pointer dereference.

Fixes #9133.

LGTM=dneil
R=dneil
CC=dvyukov, golang-codereviews, iant
https://golang.org/cl/179980043
      378c2515
    • Russ Cox's avatar
      undo CL 131750044 / 2d6d44ceb80e · 2d53d6b5
      Russ Cox authored 
      Breaks reading from stdin in parent after exec with SysProcAttr{Setpgid: true}.

package main

import (
        "fmt"
        "os"
        "os/exec"
        "syscall"
)

func main() {
        cmd := exec.Command("true")
        cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
        cmd.Run()

        fmt.Printf("Hit enter:")
        os.Stdin.Read(make([]byte, 100))
        fmt.Printf("Bye\n")
}

In go1.3, I type enter at the prompt and the program exits.
With the CL being rolled back, the program wedges at the
prompt.

««« original CL description
syscall: SysProcAttr job control changes

Making the child's process group the foreground process group and
placing the child in a specific process group involves co-ordination
between the parent and child that must be done post-fork but pre-exec.

LGTM=iant
R=golang-codereviews, gobot, iant, mikioh.mikioh
CC=golang-codereviews
https://golang.org/cl/131750044

»»»

LGTM=minux, dneil
R=dneil, minux
CC=golang-codereviews, iant, michael.p.macinnis
https://golang.org/cl/174450043
      2d53d6b5
  11. 18 Nov, 2014 1 commit
  13. 17 Nov, 2014 8 commits
  15. 16 Nov, 2014 2 commits
    • Russ Cox's avatar
      runtime: fix sudog leak · b3932bab
      Russ Cox authored 
      The SudoG used to sit on the stack, so it was cheap to allocated
and didn't need to be cleaned up when finished.

For the conversion to Go, we had to move sudog off the stack
for a few reasons, so we added a cache of recently used sudogs
to keep allocation cheap. But we didn't add any of the necessary
cleanup before adding a SudoG to the new cache, and so the cached
SudoGs had stale pointers inside them that have caused all sorts
of awful, hard to debug problems.

CL 155760043 made sure SudoG.elem is cleaned up.
CL 150520043 made sure SudoG.selectdone is cleaned up.

This CL makes sure SudoG.next, SudoG.prev, and SudoG.waitlink
are cleaned up. I should have done this when I did the other two
fields; instead I wasted a week tracking down a leak they caused.

A dangling SudoG.waitlink can point into a sudogcache list that
has been "forgotten" in order to let the GC collect it, but that
dangling .waitlink keeps the list from being collected.
And then the list holding the SudoG with the dangling waitlink
can find itself in the same situation, and so on. We end up
with lists of lists of unusable SudoGs that are still linked into
the object graph and never collected (given the right mix of
non-trivial selects and non-channel synchronization).

More details in golang.org/issue/9110.

Fixes #9110.

LGTM=r
R=r
CC=dvyukov, golang-codereviews, iant, khr
https://golang.org/cl/177870043
      b3932bab
    • Russ Cox's avatar
      runtime: update URL for heap dump format · 6150414c
      Russ Cox authored 
      I just created that redirect, so we can change
it once the wiki moves.

LGTM=bradfitz, khr
R=khr, bradfitz
CC=golang-codereviews
https://golang.org/cl/177780043
      6150414c
  17. 14 Nov, 2014 3 commits
  19. 12 Nov, 2014 4 commits
  21. 11 Nov, 2014 3 commits
    • Robert Griesemer's avatar
      spec: method selectors don't auto-deref named pointer types · 40818cfe
      Robert Griesemer authored 
      Language clarification.

The existing rules for selector expressions imply
automatic dereferencing of pointers to struct fields.
They also implied automatic dereferencing of selectors
denoting methods. In almost all cases, such automatic
dereferencing does indeed take place for methods but the
reason is not the selector rules but the fact that method
sets include both methods with T and *T receivers; so for
a *T actual receiver, a method expecting a formal T
receiver, also accepts a *T (and the invocation or method
value expression is the reason for the auto-derefering).

However, the rules as stated so far implied that even in
case of a variable p of named pointer type P, a selector
expression p.f would always be shorthand for (*p).f. This
is true for field selectors f, but cannot be true for
method selectors since a named pointer type always has an
empty method set.

Named pointer types may never appear as anonymous field
types (and method receivers, for that matter), so this
only applies to variables declared of a named pointer
type. This is exceedingly rare and perhaps shouldn't be
permitted in the first place (but we cannot change that).

Amended the selector rules to make auto-deref of values
of named pointer types an exception to the general rules
and added corresponding examples with explanations.

Both gc and gccgo have a bug where they do auto-deref
pointers of named types in method selectors where they
should not:

See http://play.golang.org/p/c6VhjcIVdM , line 45.

Fixes #5769.
Fixes #8989.

LGTM=r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/168790043
      40818cfe
    • Rob Pike's avatar
      doc/gopher: add jpgs of the 5th anniversary image · 0f8cd143
      Rob Pike authored 
      LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://golang.org/cl/172980043
      0f8cd143
    • Nigel Tao's avatar
      doc: update go1.4.html's minor library changes. · e522a477
      Nigel Tao authored 
      LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/173920043
      e522a477
  23. 10 Nov, 2014 8 commits