author | Shawn Walker-Salas <shawn.walker@oracle.com> |
Thu, 14 Apr 2016 12:48:37 -0700 | |
changeset 5781 | ecbdf40c0a37 |
parent 5331 | 9c955076ffe3 |
permissions | -rw-r--r-- |
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From 08ea82529a12506da7b329c2d0f6af57b714514a Mon Sep 17 00:00:00 2001 |
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From: Austin Clements <[email protected]> |
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Date: Wed, 18 Nov 2015 14:10:40 -0500 |
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Subject: [PATCH 48/63] [release-branch.go1.5] runtime: prevent sigprof during |
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all stack barrier ops |
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A sigprof during stack barrier insertion or removal can crash if it |
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detects an inconsistency between the stkbar array and the stack |
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itself. Currently we protect against this when scanning another G's |
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stack using stackLock, but we don't protect against it when unwinding |
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stack barriers for a recover or a memmove to the stack. |
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This commit cleans up and improves the stack locking code. It |
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abstracts out the lock and unlock operations. It uses the lock |
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consistently everywhere we perform stack operations, and pushes the |
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lock/unlock down closer to where the stack barrier operations happen |
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to make it more obvious what it's protecting. Finally, it modifies |
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sigprof so that instead of spinning until it acquires the lock, it |
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simply doesn't perform a traceback if it can't acquire it. This is |
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necessary to prevent self-deadlock. |
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|
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Updates #11863, which introduced stackLock to fix some of these |
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issues, but didn't go far enough. |
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Updates #12528. |
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Change-Id: I9d1fa88ae3744d31ba91500c96c6988ce1a3a349 |
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Reviewed-on: https://go-review.googlesource.com/17036 |
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Reviewed-by: Russ Cox <[email protected]> |
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Run-TryBot: Austin Clements <[email protected]> |
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TryBot-Result: Gobot Gobot <[email protected]> |
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Reviewed-on: https://go-review.googlesource.com/17057 |
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--- |
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src/runtime/mgcmark.go | 33 +++++++++++++++++++++++++++++++++ |
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src/runtime/proc1.go | 25 +++++++++++++------------ |
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2 files changed, 46 insertions(+), 12 deletions(-) |
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diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go |
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index 64cc1af..ac93e16 100644 |
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--- a/src/runtime/mgcmark.go |
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+++ b/src/runtime/mgcmark.go |
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@@ -365,6 +365,8 @@ func scanstack(gp *g) { |
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throw("g already has stack barriers") |
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} |
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+ gcLockStackBarriers(gp) |
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+ |
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case _GCmarktermination: |
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if int(gp.stkbarPos) == len(gp.stkbar) { |
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// gp hit all of the stack barriers (or there |
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@@ -419,6 +421,9 @@ func scanstack(gp *g) { |
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if gcphase == _GCmarktermination { |
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gcw.dispose() |
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} |
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+ if gcphase == _GCscan { |
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+ gcUnlockStackBarriers(gp) |
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+ } |
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gp.gcscanvalid = true |
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} |
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|
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@@ -572,6 +577,8 @@ func gcRemoveStackBarriers(gp *g) { |
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print("hit ", gp.stkbarPos, " stack barriers, goid=", gp.goid, "\n") |
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} |
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+ gcLockStackBarriers(gp) |
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+ |
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// Remove stack barriers that we didn't hit. |
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for _, stkbar := range gp.stkbar[gp.stkbarPos:] { |
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gcRemoveStackBarrier(gp, stkbar) |
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@@ -581,6 +588,8 @@ func gcRemoveStackBarriers(gp *g) { |
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// adjust them. |
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gp.stkbarPos = 0 |
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gp.stkbar = gp.stkbar[:0] |
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+ |
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+ gcUnlockStackBarriers(gp) |
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} |
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|
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// gcRemoveStackBarrier removes a single stack barrier. It is the |
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@@ -627,6 +636,7 @@ func gcPrintStkbars(stkbar []stkbar) { |
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// |
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//go:nosplit |
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func gcUnwindBarriers(gp *g, sp uintptr) { |
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+ gcLockStackBarriers(gp) |
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// On LR machines, if there is a stack barrier on the return |
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// from the frame containing sp, this will mark it as hit even |
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// though it isn't, but it's okay to be conservative. |
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@@ -635,6 +645,7 @@ func gcUnwindBarriers(gp *g, sp uintptr) { |
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gcRemoveStackBarrier(gp, gp.stkbar[gp.stkbarPos]) |
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gp.stkbarPos++ |
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} |
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+ gcUnlockStackBarriers(gp) |
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if debugStackBarrier && gp.stkbarPos != before { |
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print("skip barriers below ", hex(sp), " in goid=", gp.goid, ": ") |
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gcPrintStkbars(gp.stkbar[before:gp.stkbarPos]) |
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@@ -658,6 +669,28 @@ func setNextBarrierPC(pc uintptr) { |
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gp.stkbar[gp.stkbarPos].savedLRVal = pc |
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} |
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|
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+// gcLockStackBarriers synchronizes with tracebacks of gp's stack |
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+// during sigprof for installation or removal of stack barriers. It |
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+// blocks until any current sigprof is done tracebacking gp's stack |
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+// and then disallows profiling tracebacks of gp's stack. |
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+// |
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+// This is necessary because a sigprof during barrier installation or |
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+// removal could observe inconsistencies between the stkbar array and |
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+// the stack itself and crash. |
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+func gcLockStackBarriers(gp *g) { |
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+ for !cas(&gp.stackLock, 0, 1) { |
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+ osyield() |
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+ } |
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+} |
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+ |
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+func gcTryLockStackBarriers(gp *g) bool { |
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+ return cas(&gp.stackLock, 0, 1) |
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+} |
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+ |
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+func gcUnlockStackBarriers(gp *g) { |
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+ atomicstore(&gp.stackLock, 0) |
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+} |
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+ |
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// TODO(austin): Can we consolidate the gcDrain* functions? |
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|
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// gcDrain scans objects in work buffers, blackening grey |
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diff --git a/src/runtime/proc1.go b/src/runtime/proc1.go |
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index 55f1a24..54cb3eb 100644 |
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--- a/src/runtime/proc1.go |
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+++ b/src/runtime/proc1.go |
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@@ -414,13 +414,7 @@ func scang(gp *g) { |
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// the goroutine until we're done. |
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if castogscanstatus(gp, s, s|_Gscan) { |
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if !gp.gcscandone { |
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- // Coordinate with traceback |
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- // in sigprof. |
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- for !cas(&gp.stackLock, 0, 1) { |
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- osyield() |
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- } |
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scanstack(gp) |
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- atomicstore(&gp.stackLock, 0) |
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gp.gcscandone = true |
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140 |
} |
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restartg(gp) |
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@@ -2500,11 +2494,6 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { |
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// Profiling runs concurrently with GC, so it must not allocate. |
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mp.mallocing++ |
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145 |
|
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- // Coordinate with stack barrier insertion in scanstack. |
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- for !cas(&gp.stackLock, 0, 1) { |
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- osyield() |
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- } |
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150 |
- |
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// Define that a "user g" is a user-created goroutine, and a "system g" |
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// is one that is m->g0 or m->gsignal. |
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153 |
// |
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154 |
@@ -2571,8 +2560,18 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { |
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// transition. We simply require that g and SP match and that the PC is not |
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156 |
// in gogo. |
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157 |
traceback := true |
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158 |
+ haveStackLock := false |
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159 |
if gp == nil || sp < gp.stack.lo || gp.stack.hi < sp || setsSP(pc) { |
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160 |
traceback = false |
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161 |
+ } else if gp.m.curg != nil { |
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162 |
+ if gcTryLockStackBarriers(gp.m.curg) { |
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163 |
+ haveStackLock = true |
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164 |
+ } else { |
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165 |
+ // Stack barriers are being inserted or |
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166 |
+ // removed, so we can't get a consistent |
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167 |
+ // traceback right now. |
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168 |
+ traceback = false |
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169 |
+ } |
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170 |
} |
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171 |
var stk [maxCPUProfStack]uintptr |
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172 |
n := 0 |
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173 |
@@ -2615,7 +2614,9 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { |
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174 |
} |
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175 |
} |
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176 |
} |
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177 |
- atomicstore(&gp.stackLock, 0) |
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178 |
+ if haveStackLock { |
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179 |
+ gcUnlockStackBarriers(gp.m.curg) |
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180 |
+ } |
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181 |
|
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182 |
if prof.hz != 0 { |
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183 |
// Simple cas-lock to coordinate with setcpuprofilerate. |
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184 |
-- |
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185 |
2.6.1 |
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186 |