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runtime: improve diagnostics for "scan missed a g"

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Currently there are no diagnostics for mark root check during marking.
Fix this by printing out the same diagnostics we print during mark
termination.

Also, drop the allglock before throwing. Holding that across a throw
causes a self-deadlock with tracebackothers.

For #16083.

Change-Id: Ib605f3ae0c17e70704b31d8378274cfaa2307dc2
Reviewed-on: https://go-review.googlesource.com/33339
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2016-11-17 10:48:40 -05:00
parent 7061dc3f6e
commit 05dc6b26ca
1 changed files with 14 additions and 8 deletions
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22
src/runtime/mgcmark.go
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@ -126,26 +126,32 @@ func gcMarkRootCheck() {
lock(&allglock) lock(&allglock)
// Check that stacks have been scanned. // Check that stacks have been scanned.
var gp *g
if gcphase == _GCmarktermination && debug.gcrescanstacks > 0 { if gcphase == _GCmarktermination && debug.gcrescanstacks > 0 {
for i := 0; i < len(allgs); i++ { for i := 0; i < len(allgs); i++ {
gp := allgs[i] gp = allgs[i]
if !(gp.gcscandone && gp.gcscanvalid) && readgstatus(gp) != _Gdead { if !(gp.gcscandone && gp.gcscanvalid) && readgstatus(gp) != _Gdead {
println("gp", gp, "goid", gp.goid, goto fail
"status", readgstatus(gp),
"gcscandone", gp.gcscandone,
"gcscanvalid", gp.gcscanvalid)
throw("scan missed a g")
} }
} }
} else { } else {
for i := 0; i < work.nStackRoots; i++ { for i := 0; i < work.nStackRoots; i++ {
gp := allgs[i] gp = allgs[i]
if !gp.gcscandone { if !gp.gcscandone {
throw("scan missed a g") goto fail
} }
} }
} }
unlock(&allglock) unlock(&allglock)
return
fail:
println("gp", gp, "goid", gp.goid,
"status", readgstatus(gp),
"gcscandone", gp.gcscandone,
"gcscanvalid", gp.gcscanvalid)
unlock(&allglock) // Avoid self-deadlock with traceback.
throw("scan missed a g")
} }
// ptrmask for an allocation containing a single pointer. // ptrmask for an allocation containing a single pointer.