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runtime: move mem profile sampling into m-acquired section

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It was not safe to do mcache profiling updates outside the critical
section, but we got lucky because the runtime was not preemptible.
Adding chunked memory clearing (CL 270943) created preemption
opportunities, which led to corruption of runtime data structures.

Fixes #47304.
Fixes #47302.

Change-Id: I461615470d62328a83ccbac537fbdc6dcde81c85
Reviewed-on: https://go-review.googlesource.com/c/go/+/336449
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
David Chase 2021-07-21 18:38:05 -04:00
parent 3e48c0381f
commit fdb45acd1f
1 changed files with 9 additions and 11 deletions
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20
src/runtime/malloc.go
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@ -1135,13 +1135,21 @@ func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
msanmalloc(x, size)
}
if rate := MemProfileRate; rate > 0 {
// Note cache c only valid while m acquired; see #47302
if rate != 1 && size < c.nextSample {
c.nextSample -= size
} else {
profilealloc(mp, x, size)
}
}
mp.mallocing = 0
releasem(mp)
// Pointerfree data can be zeroed late in a context where preemption can occur.
// x will keep the memory alive.
if !isZeroed && needzero {
memclrNoHeapPointersChunked(size, x)
memclrNoHeapPointersChunked(size, x) // This is a possible preemption point: see #47302
}
if debug.malloc {
@ -1155,16 +1163,6 @@ func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
}
}
if rate := MemProfileRate; rate > 0 {
if rate != 1 && size < c.nextSample {
c.nextSample -= size
} else {
mp := acquirem()
profilealloc(mp, x, size)
releasem(mp)
}
}
if assistG != nil {
// Account for internal fragmentation in the assist
// debt now that we know it.