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  1. 29 Jul, 2015 12 commits
    • Russ Cox's avatar
      runtime: reenable bad pointer check in GC · 4addec3a
      Russ Cox authored 
      The last time we tried this, linux/arm64 broke.
The series of CLs leading to this one fixes that problem.
Let's try again.

Fixes #9880.

Change-Id: I67bc1d959175ec972d4dcbe4aa6f153790f74251
Reviewed-on: https://go-review.googlesource.com/12849Reviewed-by: default avatarBrad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: default avatarAustin Clements <austin@google.com>
      4addec3a
    • Russ Cox's avatar
      cmd/internal/obj/arm64: reject misaligned stack frames, except empty frames · 034a10d4
      Russ Cox authored 
      The layout code has to date insisted on stack frames that are 16-aligned
including the saved LR, and it ensured this by growing the frame itself.
This breaks code that refers to values near the top of the frame by positive
offset from SP, and in general it's too magical: if you see TEXT xxx, $N,
you expect that the frame size is actually N, not sometimes N and sometimes N+8.

This led to a serious bug in the compiler where ambiguously live values
were not being zeroed correctly, which in turn triggered an assertion
in the GC about finding only valid pointers. The compiler has been
fixed to always emit aligned frames, and the hand-written assembly
has also been fixed.

Now that everything is aligned, make unaligned an error instead of
something to "fix" silently.

For #9880.

Change-Id: I05f01a9df174d64b37fa19b36a6b6c5f18d5ba2d
Reviewed-on: https://go-review.googlesource.com/12848Reviewed-by: default avatarAustin Clements <austin@google.com>
      034a10d4
    • Russ Cox's avatar
      cmd/link: fix nosplit stack overflow checks · 767e0658
      Russ Cox authored 
      The nosplit stack overflow checks were confused about morestack.
The comment about not having correct SP information at the call
to morestack was true, but that was a real bug, not something to
work around. I fixed that problem in CL 12144. With that fixed,
no need to special-case morestack in the way done here.

This cleanup and simplification of the code was the first step
to fixing a bug that happened when I started working on the
arm64 frame size adjustments, but the cleanup was sufficient
to make the bug go away.

For #9880.

Change-Id: I16b69a5c16b6b8cb4090295d3029c42d606e3b9b
Reviewed-on: https://go-review.googlesource.com/12846Reviewed-by: default avatarAustin Clements <austin@google.com>
      767e0658
    • Russ Cox's avatar
      runtime, reflect: use correctly aligned stack frame sizes on arm64 · 42122057
      Russ Cox authored 
      arm64 requires either no stack frame or a frame with a size that is 8 mod 16
(adding the saved LR will make it 16-aligned).

The cmd/internal/obj/arm64 has been silently aligning frames, but it led to
a terrible bug when the compiler and obj disagreed on the frame size,
and it's just generally confusing, so we're going to make misaligned frames
an error instead of something that is silently changed.

This CL prepares by updating assembly files.
Note that the changes in this CL are already being done silently by
cmd/internal/obj/arm64, so there is no semantic effect here,
just a clarity effect.

For #9880.

Change-Id: Ibd6928dc5fdcd896c2bacd0291bf26b364591e28
Reviewed-on: https://go-review.googlesource.com/12845Reviewed-by: default avatarAustin Clements <austin@google.com>
      42122057
    • Russ Cox's avatar
      cmd/compile: align arm64 stack frames correctly · 3952057c
      Russ Cox authored 
      If the compiler doesn't do it, cmd/internal/obj/arm64 will,
and that will break the zeroing of ambiguously live values
done in zerorange, which in turn produces uninitialized
pointer cells that the GC trips over.

For #9880.

Change-Id: Ice97c30bc8b36d06b7b88d778d87fab8e1827fdc
Reviewed-on: https://go-review.googlesource.com/12847Reviewed-by: default avatarAustin Clements <austin@google.com>
      3952057c
    • Austin Clements's avatar
      runtime: report GC CPU utilization in MemStats · 23e4744c
      Austin Clements authored 
      This adds a GCCPUFraction field to MemStats that reports the
cumulative fraction of the program's execution time spent in the
garbage collector. This is equivalent to the utilization percent shown
in the gctrace output and makes this available programmatically.

This does make one small effect on the gctrace output: we now report
the duration of mark termination up to just before the final
start-the-world, rather than up to just after. However, unlike
stop-the-world, I don't believe there's any way that start-the-world
can block, so it should take negligible time.

While there are many statistics one might want to expose via MemStats,
this is one of the few that will undoubtedly remain meaningful
regardless of future changes to the memory system.

The diff for this change is larger than the actual change. Mostly it
lifts the code for computing the GC CPU utilization out of the
debug.gctrace path.

Updates #10323.

Change-Id: I0f7dc3fdcafe95e8d1233ceb79de606b48acd989
Reviewed-on: https://go-review.googlesource.com/12844Reviewed-by: default avatarRuss Cox <rsc@golang.org>
      23e4744c
    • Austin Clements's avatar
      runtime: always capture GC phase transition times · 4b71660c
      Austin Clements authored 
      Currently we only capture GC phase transition times if
debug.gctrace>0, but we're about to compute GC CPU utilization
regardless of whether debug.gctrace is set, so we need these
regardless of debug.gctrace.

Change-Id: If3acf16505a43d416e9a99753206f03287180660
Reviewed-on: https://go-review.googlesource.com/12843Reviewed-by: default avatarRuss Cox <rsc@golang.org>
Reviewed-by: default avatarRick Hudson <rlh@golang.org>
      4b71660c
    • Austin Clements's avatar
      runtime: avoid race between SIGPROF traceback and stack barriers · 87f97c73
      Austin Clements authored 
      The following sequence of events can lead to the runtime attempting an
out-of-bounds access on a stack barrier slice:

1. A SIGPROF comes in on a thread while the G on that thread is in
   _Gsyscall. The sigprof handler calls gentraceback, which saves a
   local copy of the G's stkbar slice. Currently the G has no stack
   barriers, so this slice is empty.

2. On another thread, the GC concurrently scans the stack of the
   goroutine being profiled (it considers it stopped because it's in
   _Gsyscall) and installs stack barriers.

3. Back on the sigprof thread, gentraceback comes across a stack
   barrier in the stack and attempts to look it up in its (zero
   length) copy of G's old stkbar slice, which causes an out-of-bounds
   access.

This commit fixes this by adding a simple cas spin to synchronize the
SIGPROF handler with stack barrier insertion.

In general I would prefer that this synchronization be done through
the G status, since that's how stack scans are otherwise synchronized,
but adding a new lock is a much smaller change and G statuses are full
of subtlety.

Fixes #11863.

Change-Id: Ie89614a6238bb9c6a5b1190499b0b48ec759eaf7
Reviewed-on: https://go-review.googlesource.com/12748Reviewed-by: default avatarRuss Cox <rsc@golang.org>
      87f97c73
    • Rick Hudson's avatar
      runtime: force mutator to give work buffer to GC · e95bc5fe
      Rick Hudson authored 
      The scheduler, work buffer's dispose, and write barriers
can conspire to hide the a pointer from the GC's concurent
mark phase. If this pointer is the only path to a large
amount of marking the STW mark termination phase may take
a lot of time.

Consider the following:
1) dispose places a work buffer on the partial queue
2) the GC is busy so it does not immediately remove and
   process the work buffer
3) the scheduler runs a mutator whose write barrier dequeues the
   work buffer from the partial queue so the GC won't see it
This repeats until the GC reaches the mark termination
phase where the GC finally discovers the pointer along
with a lot of work to do.

This CL fixes the problem by having the mutator
dispose of the buffer to the full queue instead of
the partial queue. Since the write buffer never asks for full
buffers the conspiracy described above is not possible.

Updates #11694.

Change-Id: I2ce832f9657a7570f800e8ce4459cd9e304ef43b
Reviewed-on: https://go-review.googlesource.com/12840Reviewed-by: default avatarAustin Clements <austin@google.com>
      e95bc5fe
    • Rob Pike's avatar
      doc: add json tokenizer to go1.5.html · ff991940
      Rob Pike authored 
      Change-Id: I45d92fed757fa1866d5b80e53ed1af6712fa6741
Reviewed-on: https://go-review.googlesource.com/12782Reviewed-by: default avatarRuss Cox <rsc@golang.org>
      ff991940
    • Mikio Hara's avatar
      cmd/internal/asm: delete · 861af804
      Mikio Hara authored 
      Updates #10510.

Change-Id: Ib4d39943969d18517b373292b83d87650d5df12a
Reviewed-on: https://go-review.googlesource.com/12787
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: default avatarBrad Fitzpatrick <bradfitz@golang.org>
      861af804
    • Rob Pike's avatar
      cmd: delete old[5689]a · ba0c142d
      Rob Pike authored 
      These are the old assemblers written in C, and now they are
not needed.

Fixes #10510.

Change-Id: Id9337ffc8eccfd93c84b2e23f427fb1a576b543d
Reviewed-on: https://go-review.googlesource.com/12784Reviewed-by: default avatarRuss Cox <rsc@golang.org>
Reviewed-by: default avatarBrad Fitzpatrick <bradfitz@golang.org>
      ba0c142d
  3. 28 Jul, 2015 23 commits
  5. 27 Jul, 2015 5 commits
    • Brad Fitzpatrick's avatar
      net/http: pause briefly after closing Server connection when body remains · a3ffd836
      Brad Fitzpatrick authored 
      From https://github.com/golang/go/issues/11745#issuecomment-123555313
this implements option (b), having the server pause slightly after
sending the final response on a TCP connection when we're about to close
it when we know there's a request body outstanding. This biases the
client (which might not be Go) to prefer our response header over the
request body write error.

Updates #11745

Change-Id: I07cb0b74519d266c8049d9e0eb23a61304eedbf8
Reviewed-on: https://go-review.googlesource.com/12658Reviewed-by: default avatarRuss Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
      a3ffd836
    • David Crawshaw's avatar
      runtime/cgo: remove TMPDIR logic for iOS · 249894ab
      David Crawshaw authored 
      Seems like the simplest solution for 1.5. All the parts of the test
suite I can run on my current device (for which my exception handler
fix no longer works, apparently) pass without this code. I'll move it
into x/mobile/app.

Fixes #11884

Change-Id: I2da40c8c7b48a4c6970c4d709dd7c148a22e8727
Reviewed-on: https://go-review.googlesource.com/12721Reviewed-by: default avatarIan Lance Taylor <iant@golang.org>
      249894ab
    • Austin Clements's avatar
      runtime: close window that hides GC work from concurrent mark · c1f7a56f
      Austin Clements authored 
      Currently we enter mark 2 by first flushing all existing gcWork caches
and then setting gcBlackenPromptly, which disables further gcWork
caching. However, if a worker or assist pulls a work buffer in to its
gcWork cache after that cache has been flushed but before caching is
disabled, that work may remain in that cache until mark termination.
If that work represents a heap bottleneck (e.g., a single pointer that
is the only way to reach a large amount of the heap), this can force
mark termination to do a large amount of work, resulting in a long
STW.

Fix this by reversing the order of these steps: first disable caching,
then flush all existing caches.

Rick Hudson <rlh> did the hard work of tracking this down. This CL
combined with CL 12672 and CL 12646 distills the critical parts of his
fix from CL 12539.

Fixes #11694.

Change-Id: Ib10d0a21e3f6170a80727d0286f9990df049fed2
Reviewed-on: https://go-review.googlesource.com/12688Reviewed-by: default avatarRick Hudson <rlh@golang.org>
      c1f7a56f
    • Austin Clements's avatar
      runtime: enable GC assists ASAP · 510fd135
      Austin Clements authored 
      Currently the GC coordinator enables GC assists at the same time it
enables background mark workers, after the concurrent scan phase is
done. However, this means a rapidly allocating mutator has the entire
scan phase during which to allocate beyond the heap trigger and
potentially beyond the heap goal with no back-pressure from assists.
This prevents the feedback system that's supposed to keep the heap
size under the heap goal from doing its job.

Fix this by enabling mutator assists during the scan phase. This is
safe because the write barrier is already enabled and globally
acknowledged at this point.

There's still a very small window between when the heap size reaches
the heap trigger and when the GC coordinator is able to stop the world
during which the mutator can allocate unabated. This allows *very*
rapidly allocator mutators like TestTraceStress to still occasionally
exceed the heap goal by a small amount (~20 MB at most for
TestTraceStress). However, this seems like a corner case.

Fixes #11677.

Change-Id: I0f80d949ec82341cd31ca1604a626efb7295a819
Reviewed-on: https://go-review.googlesource.com/12674Reviewed-by: default avatarRuss Cox <rsc@golang.org>
      510fd135
    • Austin Clements's avatar
      runtime: allow GC drain whenever write barrier is enabled · f5e67e53
      Austin Clements authored 
      Currently we hand-code a set of phases when draining is allowed.
However, this set of phases is conservative. The critical invariant is
simply that the write barrier must be enabled if we're draining.

Shortly we're going to enable mutator assists during the scan phase,
which means we may drain during the scan phase. In preparation, this
commit generalizes these assertions to check the fundamental condition
that the write barrier is enabled, rather than checking that we're in
any particular phase.

Change-Id: I0e1bec1ca823d4a697a0831ec4c50f5dd3f2a893
Reviewed-on: https://go-review.googlesource.com/12673Reviewed-by: default avatarRuss Cox <rsc@golang.org>
      f5e67e53
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