diff options
Diffstat (limited to 'src/runtime/netpoll.go')
| -rw-r--r-- | src/runtime/netpoll.go | 43 |
1 files changed, 26 insertions, 17 deletions
diff --git a/src/runtime/netpoll.go b/src/runtime/netpoll.go index 77eb3aa4c6..f296b0a4db 100644 --- a/src/runtime/netpoll.go +++ b/src/runtime/netpoll.go @@ -74,6 +74,7 @@ type pollDesc struct { // pollReset, pollWait, pollWaitCanceled and runtime·netpollready (IO readiness notification) // proceed w/o taking the lock. So closing, everr, rg, rd, wg and wd are manipulated // in a lock-free way by all operations. + // TODO(golang.org/issue/49008): audit these lock-free fields for continued correctness. // NOTE(dvyukov): the following code uses uintptr to store *g (rg/wg), // that will blow up when GC starts moving objects. lock mutex // protects the following fields @@ -82,11 +83,11 @@ type pollDesc struct { everr bool // marks event scanning error happened user uint32 // user settable cookie rseq uintptr // protects from stale read timers - rg uintptr // pdReady, pdWait, G waiting for read or nil + rg uintptr // pdReady, pdWait, G waiting for read or nil. Accessed atomically. rt timer // read deadline timer (set if rt.f != nil) rd int64 // read deadline wseq uintptr // protects from stale write timers - wg uintptr // pdReady, pdWait, G waiting for write or nil + wg uintptr // pdReady, pdWait, G waiting for write or nil. Accessed atomically. wt timer // write deadline timer wd int64 // write deadline self *pollDesc // storage for indirect interface. See (*pollDesc).makeArg. @@ -143,20 +144,22 @@ func poll_runtime_isPollServerDescriptor(fd uintptr) bool { func poll_runtime_pollOpen(fd uintptr) (*pollDesc, int) { pd := pollcache.alloc() lock(&pd.lock) - if pd.wg != 0 && pd.wg != pdReady { + wg := atomic.Loaduintptr(&pd.wg) + if wg != 0 && wg != pdReady { throw("runtime: blocked write on free polldesc") } - if pd.rg != 0 && pd.rg != pdReady { + rg := atomic.Loaduintptr(&pd.rg) + if rg != 0 && rg != pdReady { throw("runtime: blocked read on free polldesc") } pd.fd = fd pd.closing = false pd.everr = false pd.rseq++ - pd.rg = 0 + atomic.Storeuintptr(&pd.rg, 0) pd.rd = 0 pd.wseq++ - pd.wg = 0 + atomic.Storeuintptr(&pd.wg, 0) pd.wd = 0 pd.self = pd unlock(&pd.lock) @@ -171,10 +174,12 @@ func poll_runtime_pollClose(pd *pollDesc) { if !pd.closing { throw("runtime: close polldesc w/o unblock") } - if pd.wg != 0 && pd.wg != pdReady { + wg := atomic.Loaduintptr(&pd.wg) + if wg != 0 && wg != pdReady { throw("runtime: blocked write on closing polldesc") } - if pd.rg != 0 && pd.rg != pdReady { + rg := atomic.Loaduintptr(&pd.rg) + if rg != 0 && rg != pdReady { throw("runtime: blocked read on closing polldesc") } netpollclose(pd.fd) @@ -198,9 +203,9 @@ func poll_runtime_pollReset(pd *pollDesc, mode int) int { return errcode } if mode == 'r' { - pd.rg = 0 + atomic.Storeuintptr(&pd.rg, 0) } else if mode == 'w' { - pd.wg = 0 + atomic.Storeuintptr(&pd.wg, 0) } return pollNoError } @@ -410,6 +415,8 @@ func netpollgoready(gp *g, traceskip int) { // returns true if IO is ready, or false if timedout or closed // waitio - wait only for completed IO, ignore errors +// Concurrent calls to netpollblock in the same mode are forbidden, as pollDesc +// can hold only a single waiting goroutine for each mode. func netpollblock(pd *pollDesc, mode int32, waitio bool) bool { gpp := &pd.rg if mode == 'w' { @@ -418,17 +425,19 @@ func netpollblock(pd *pollDesc, mode int32, waitio bool) bool { // set the gpp semaphore to pdWait for { - old := *gpp - if old == pdReady { - *gpp = 0 + // Consume notification if already ready. + if atomic.Casuintptr(gpp, pdReady, 0) { return true } - if old != 0 { - throw("runtime: double wait") - } if atomic.Casuintptr(gpp, 0, pdWait) { break } + + // Double check that this isn't corrupt; otherwise we'd loop + // forever. + if v := atomic.Loaduintptr(gpp); v != pdReady && v != 0 { + throw("runtime: double wait") + } } // need to recheck error states after setting gpp to pdWait @@ -452,7 +461,7 @@ func netpollunblock(pd *pollDesc, mode int32, ioready bool) *g { } for { - old := *gpp + old := atomic.Loaduintptr(gpp) if old == pdReady { return nil } |