Merge release-20201030.0-41-g53eeb06ef (automated)

2 files changed, 29 insertions, 24 deletions

diff --git a/pkg/sentry/syscalls/linux/sys_splice.go b/pkg/sentry/syscalls/linux/sys_splice.go
index 46616c961..1c4cdb0dd 100644
--- a/pkg/sentry/syscalls/linux/sys_splice.go
+++ b/pkg/sentry/syscalls/linux/sys_splice.go
@@ -41,6 +41,7 @@ func doSplice(t *kernel.Task, outFile, inFile *fs.File, opts fs.SpliceOpts, nonB
 		inCh  chan struct{}
 		outCh chan struct{}
 	)
+
 	for opts.Length > 0 {
 		n, err = fs.Splice(t, outFile, inFile, opts)
 		opts.Length -= n
@@ -61,23 +62,28 @@ func doSplice(t *kernel.Task, outFile, inFile *fs.File, opts fs.SpliceOpts, nonB
 				inW, _ := waiter.NewChannelEntry(inCh)
 				inFile.EventRegister(&inW, EventMaskRead)
 				defer inFile.EventUnregister(&inW)
-				continue // Need to refresh readiness.
+				// Need to refresh readiness.
+				continue
 			}
 			if err = t.Block(inCh); err != nil {
 				break
 			}
 		}
-		if outFile.Readiness(EventMaskWrite) == 0 {
-			if outCh == nil {
-				outCh = make(chan struct{}, 1)
-				outW, _ := waiter.NewChannelEntry(outCh)
-				outFile.EventRegister(&outW, EventMaskWrite)
-				defer outFile.EventUnregister(&outW)
-				continue // Need to refresh readiness.
-			}
-			if err = t.Block(outCh); err != nil {
-				break
-			}
+		// Don't bother checking readiness of the outFile, because it's not a
+		// guarantee that it won't return EWOULDBLOCK. Both pipes and eventfds
+		// can be "ready" but will reject writes of certain sizes with
+		// EWOULDBLOCK.
+		if outCh == nil {
+			outCh = make(chan struct{}, 1)
+			outW, _ := waiter.NewChannelEntry(outCh)
+			outFile.EventRegister(&outW, EventMaskWrite)
+			defer outFile.EventUnregister(&outW)
+			// We might be ready to write now. Try again before
+			// blocking.
+			continue
+		}
+		if err = t.Block(outCh); err != nil {
+			break
 		}
 	}
 
diff --git a/pkg/sentry/syscalls/linux/vfs2/splice.go b/pkg/sentry/syscalls/linux/vfs2/splice.go
index 035e2a6b0..9ce4f280a 100644
--- a/pkg/sentry/syscalls/linux/vfs2/splice.go
+++ b/pkg/sentry/syscalls/linux/vfs2/splice.go
@@ -480,18 +480,17 @@ func (dw *dualWaiter) waitForBoth(t *kernel.Task) error {
 
 // waitForOut waits for dw.outfile to be read.
 func (dw *dualWaiter) waitForOut(t *kernel.Task) error {
-	if dw.outFile.Readiness(eventMaskWrite)&eventMaskWrite == 0 {
-		if dw.outCh == nil {
-			dw.outW, dw.outCh = waiter.NewChannelEntry(nil)
-			dw.outFile.EventRegister(&dw.outW, eventMaskWrite)
-			// We might be ready now. Try again before blocking.
-			return nil
-		}
-		if err := t.Block(dw.outCh); err != nil {
-			return err
-		}
-	}
-	return nil
+	// Don't bother checking readiness of the outFile, because it's not a
+	// guarantee that it won't return EWOULDBLOCK. Both pipes and eventfds
+	// can be "ready" but will reject writes of certain sizes with
+	// EWOULDBLOCK. See b/172075629, b/170743336.
+	if dw.outCh == nil {
+		dw.outW, dw.outCh = waiter.NewChannelEntry(nil)
+		dw.outFile.EventRegister(&dw.outW, eventMaskWrite)
+		// We might be ready to write now. Try again before blocking.
+		return nil
+	}
+	return t.Block(dw.outCh)
 }
 
 // destroy cleans up resources help by dw. No more calls to wait* can occur