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runtime/debug: avoid overflow in SetMaxThreads

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Fixes #16076

Change-Id: I91fa87b642592ee4604537dd8c3197cd61ec8b31
Reviewed-on: https://go-review.googlesource.com/31516
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Alberto Donizetti 2016-10-20 11:24:51 +02:00 committed by Ian Lance Taylor
parent f6f3aef53f
commit 10560afb54
2 changed files with 18 additions and 1 deletions
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13
src/runtime/debug/garbage_test.go
View File

@ -114,3 +114,16 @@ func TestSetGCPercent(t *testing.T) {
t.Errorf("SetGCPercent(123); SetGCPercent(x) = %d, want 123", new)
}
}
func TestSetMaxThreadsOvf(t *testing.T) {
// Verify that a big threads count will not overflow the int32
// maxmcount variable, causing a panic (see Issue 16076).
//
// This can only happen when ints are 64 bits, since on platforms
// with 32 bit ints SetMaxThreads (which takes an int parameter)
// cannot be given anything that will overflow an int32.
//
// Call SetMaxThreads with 1<<31, but only on 64 bit systems.
nt := SetMaxThreads(1 << (30 + ^uint(0)>>63))
SetMaxThreads(nt) // restore previous value
}

6
src/runtime/proc.go
View File

@ -4294,7 +4294,11 @@ func runqsteal(_p_, p2 *p, stealRunNextG bool) *g {
func setMaxThreads(in int) (out int) {
lock(&sched.lock)
out = int(sched.maxmcount)
sched.maxmcount = int32(in)
if in > 0x7fffffff { // MaxInt32
sched.maxmcount = 0x7fffffff
} else {
sched.maxmcount = int32(in)
}
checkmcount()
unlock(&sched.lock)
return