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| author | Austin Clements <austin@google.com> | 2016-02-15 16:50:12 -0500 |
|---|---|---|
| committer | Austin Clements <austin@google.com> | 2016-02-25 23:37:17 +0000 |
| commit | 1e91e2a25a0058cc25b3836b59a0954c6c75a62c (patch) | |
| tree | 46ceeacaa14a26b6052078eff830e74b7e0176b5 /src | |
| parent | 39f2bd737bb0b9446b4d241aa76fcb87d7e77278 (diff) | |
| download | go-git-1e91e2a25a0058cc25b3836b59a0954c6c75a62c.tar.gz | |
runtime: document non-obvious requirement on sudog.elem
The channel code must not allow stack splits between when it assigns a
potential stack pointer to sudog.elem (or sudog.selectdone) and when
it makes the sudog visible to copystack by putting it on the g.waiting
list. We do get this right everywhere, but add a comment about this
subtlety for future eyes.
Change-Id: I941da150437167acff37b0e56983c793f40fcf79
Reviewed-on: https://go-review.googlesource.com/19632
Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Diffstat (limited to 'src')
| -rw-r--r-- | src/runtime/chan.go | 4 | ||||
| -rw-r--r-- | src/runtime/select.go | 2 |
2 files changed, 6 insertions, 0 deletions
diff --git a/src/runtime/chan.go b/src/runtime/chan.go index 063c5ce391..f6f3ce4d90 100644 --- a/src/runtime/chan.go +++ b/src/runtime/chan.go @@ -203,6 +203,8 @@ func chansend(t *chantype, c *hchan, ep unsafe.Pointer, block bool, callerpc uin if t0 != 0 { mysg.releasetime = -1 } + // No stack splits between assigning elem and enqueuing mysg + // on gp.waiting where copystack can find it. mysg.elem = ep mysg.waitlink = nil mysg.g = gp @@ -460,6 +462,8 @@ func chanrecv(t *chantype, c *hchan, ep unsafe.Pointer, block bool) (selected, r if t0 != 0 { mysg.releasetime = -1 } + // No stack splits between assigning elem and enqueuing mysg + // on gp.waiting where copystack can find it. mysg.elem = ep mysg.waitlink = nil gp.waiting = mysg diff --git a/src/runtime/select.go b/src/runtime/select.go index b6c3fea001..b315dde6c6 100644 --- a/src/runtime/select.go +++ b/src/runtime/select.go @@ -370,6 +370,8 @@ loop: sg.g = gp // Note: selectdone is adjusted for stack copies in stack1.go:adjustsudogs sg.selectdone = (*uint32)(noescape(unsafe.Pointer(&done))) + // No stack splits between assigning elem and enqueuing + // sg on gp.waiting where copystack can find it. sg.elem = cas.elem sg.releasetime = 0 if t0 != 0 { |