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Michael Pratt 1b072b3ed5 runtime: consistently access pollDesc r/w Gs with atomics
Both netpollblock and netpollunblock read gpp using a non-atomic load.
When consuming a ready event, netpollblock clears gpp using a non-atomic
store, thus skipping a barrier.

Thus on systems with weak memory ordering, a sequence like so this is
possible:

             T1                                T2

1. netpollblock: read gpp -> pdReady
2. netpollblock: store gpp -> 0

                                 3. netpollunblock: read gpp -> pdReady
                                 4. netpollunblock: return

i.e., without a happens-before edge between (2) and (3), netpollunblock
may read the stale value of gpp.

Switch these access to use atomic loads and stores in order to create
these edges.

For ease of future maintainance, I've simply changed rg and wg to always
be accessed atomically, though I don't believe pollOpen or pollClose
require atomics today.

Fixes #48925

Change-Id: I903ea667eea320277610b4f969129935731520c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/355952
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: David Chase <drchase@google.com>
2021-10-15 20:34:15 +00:00
.github .github: update IRC server 2021-09-30 19:56:27 +00:00
api cmd/go: stamp VCS revision and uncommitted status into binaries 2021-10-14 18:44:37 +00:00
doc doc/go1.18: add release notes for build and VCS info 2021-10-15 20:29:48 +00:00
lib/time lib/time: fix RFC 6557 url 2021-08-15 02:18:46 +00:00
misc cmd/link: disable weak reference in itab if build with "-linkshared" 2021-10-13 15:12:46 +00:00
src runtime: consistently access pollDesc r/w Gs with atomics 2021-10-15 20:34:15 +00:00
test cmd/compile: make for loops with range statements not terminating 2021-10-15 19:54:44 +00:00
.gitattributes all: treat all files as binary, but check in .bat with CRLF 2020-06-08 15:31:43 +00:00
.gitignore internal/buildcfg: move build configuration out of cmd/internal/objabi 2021-04-16 19:20:53 +00:00
AUTHORS A+C: update name to real name and add to AUTHORS 2021-09-16 23:57:28 +00:00
codereview.cfg codereview.cfg: add codereview.cfg for master branch 2021-02-19 18:44:53 +00:00
CONTRIBUTING.md all: restore changes from faulty merge/revert 2018-02-12 20:13:59 +00:00
CONTRIBUTORS A+C: update name to real name and add to AUTHORS 2021-09-16 23:57:28 +00:00
LICENSE
PATENTS
README.md README.md: update contribute URL 2021-09-30 13:33:21 +00:00
SECURITY.md SECURITY.md: update go versions 2019-09-26 15:34:57 +00:00

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