Don't call kernel.Task.Block() from netstack.SocketOperations.Write().

kernel.Task.Block() requires that the caller is running on the task goroutine.
netstack.SocketOperations.Write() uses kernel.TaskFromContext() to call
kernel.Task.Block() even if it's not running on the task goroutine. Stop doing
that.

PiperOrigin-RevId: 311178335

pkg/amutex/BUILD

@@ -6,6 +6,7 @@ go_library(
     name = "amutex",
     srcs = ["amutex.go"],
     visibility = ["//:sandbox"],
+    deps = ["//pkg/syserror"],
 )
 
 go_test(

pkg/amutex/amutex.go

@@ -18,6 +18,8 @@ package amutex
 
 import (
 	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/syserror"
 )
 
 // Sleeper must be implemented by users of the abortable mutex to allow for
@@ -53,6 +55,21 @@ func (NoopSleeper) SleepFinish(success bool) {}
 // Interrupted implements Sleeper.Interrupted.
 func (NoopSleeper) Interrupted() bool { return false }
 
+// Block blocks until either receiving from ch succeeds (in which case it
+// returns nil) or sleeper is interrupted (in which case it returns
+// syserror.ErrInterrupted).
+func Block(sleeper Sleeper, ch <-chan struct{}) error {
+	cancel := sleeper.SleepStart()
+	select {
+	case <-ch:
+		sleeper.SleepFinish(true)
+		return nil
+	case <-cancel:
+		sleeper.SleepFinish(false)
+		return syserror.ErrInterrupted
+	}
+}
+
 // AbortableMutex is an abortable mutex. It allows Lock() to be aborted while it
 // waits to acquire the mutex.
 type AbortableMutex struct {

pkg/sentry/socket/netstack/BUILD

@@ -18,6 +18,7 @@ go_library(
     ],
     deps = [
         "//pkg/abi/linux",
+        "//pkg/amutex",
         "//pkg/binary",
         "//pkg/context",
         "//pkg/log",

pkg/sentry/socket/netstack/netstack.go

@@ -34,6 +34,7 @@ import (
 	"time"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/amutex"
 	"gvisor.dev/gvisor/pkg/binary"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/log"
@@ -553,11 +554,9 @@ func (s *SocketOperations) Write(ctx context.Context, _ *fs.File, src usermem.IO
 	}
 
 	if resCh != nil {
-		t := kernel.TaskFromContext(ctx)
-		if err := t.Block(resCh); err != nil {
-			return 0, syserr.FromError(err).ToError()
+		if err := amutex.Block(ctx, resCh); err != nil {
+			return 0, err
 		}
-
 		n, _, err = s.Endpoint.Write(f, tcpip.WriteOptions{})
 	}
 
@@ -626,11 +625,9 @@ func (s *SocketOperations) ReadFrom(ctx context.Context, _ *fs.File, r io.Reader
 	}
 
 	if resCh != nil {
-		t := kernel.TaskFromContext(ctx)
-		if err := t.Block(resCh); err != nil {
-			return 0, syserr.FromError(err).ToError()
+		if err := amutex.Block(ctx, resCh); err != nil {
+			return 0, err
 		}
-
 		n, _, err = s.Endpoint.Write(f, tcpip.WriteOptions{
 			Atomic: true, // See above.
 		})

pkg/sentry/socket/netstack/netstack_vfs2.go

@@ -16,6 +16,7 @@ package netstack
 
 import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/amutex"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/sockfs"
@@ -89,11 +90,6 @@ func (s *SocketVFS2) EventUnregister(e *waiter.Entry) {
 	s.socketOpsCommon.EventUnregister(e)
 }
 
-// PRead implements vfs.FileDescriptionImpl.
-func (s *SocketVFS2) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
-	return 0, syserror.ESPIPE
-}
-
 // Read implements vfs.FileDescriptionImpl.
 func (s *SocketVFS2) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
 	// All flags other than RWF_NOWAIT should be ignored.
@@ -115,11 +111,6 @@ func (s *SocketVFS2) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.
 	return int64(n), nil
 }
 
-// PWrite implements vfs.FileDescriptionImpl.
-func (s *SocketVFS2) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
-	return 0, syserror.ESPIPE
-}
-
 // Write implements vfs.FileDescriptionImpl.
 func (s *SocketVFS2) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
 	// All flags other than RWF_NOWAIT should be ignored.
@@ -135,11 +126,9 @@ func (s *SocketVFS2) Write(ctx context.Context, src usermem.IOSequence, opts vfs
 	}
 
 	if resCh != nil {
-		t := kernel.TaskFromContext(ctx)
-		if err := t.Block(resCh); err != nil {
-			return 0, syserr.FromError(err).ToError()
+		if err := amutex.Block(ctx, resCh); err != nil {
+			return 0, err
 		}
-
 		n, _, err = s.Endpoint.Write(f, tcpip.WriteOptions{})
 	}