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net: fix race in (*resolverConfig).tryUpdate

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Fixes #14072.

Change-Id: Ie31caa06690ac621906fc5acd34da2efa4e2049f
Reviewed-on: https://go-review.googlesource.com/18860
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
This commit is contained in:
Matthew Dempsky 2016-01-22 13:31:57 -08:00
parent 315f4c70f1
commit 5efbdd9d10
3 changed files with 27 additions and 25 deletions
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22
src/net/dnsclient_unix.go
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@ -229,7 +229,6 @@ type resolverConfig struct {
// time to recheck resolv.conf.
ch chan struct{} // guards lastChecked and modTime
lastChecked time.Time // last time resolv.conf was checked
modTime time.Time // time of resolv.conf modification
mu sync.RWMutex // protects dnsConfig
dnsConfig *dnsConfig // parsed resolv.conf structure used in lookups
@ -239,16 +238,12 @@ var resolvConf resolverConfig
// init initializes conf and is only called via conf.initOnce.
func (conf *resolverConfig) init() {
// Set dnsConfig, modTime, and lastChecked so we don't parse
// Set dnsConfig and lastChecked so we don't parse
// resolv.conf twice the first time.
conf.dnsConfig = systemConf().resolv
if conf.dnsConfig == nil {
conf.dnsConfig = dnsReadConfig("/etc/resolv.conf")
}
if fi, err := os.Stat("/etc/resolv.conf"); err == nil {
conf.modTime = fi.ModTime()
}
conf.lastChecked = time.Now()
// Prepare ch so that only one update of resolverConfig may
@ -274,17 +269,12 @@ func (conf *resolverConfig) tryUpdate(name string) {
}
conf.lastChecked = now
var mtime time.Time
if fi, err := os.Stat(name); err == nil {
if fi.ModTime().Equal(conf.modTime) {
return
}
conf.modTime = fi.ModTime()
} else {
// If modTime wasn't set prior, assume nothing has changed.
if conf.modTime.IsZero() {
return
}
conf.modTime = time.Time{}
mtime = fi.ModTime()
}
if mtime.Equal(conf.dnsConfig.mtime) {
return
}
dnsConf := dnsReadConfig(name)