github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/kernel/pipe/pipe_unsafe.go (about)

     1  // Copyright 2019 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package pipe
    16  
    17  import (
    18  	"unsafe"
    19  )
    20  
    21  // lockTwoPipes locks both x.mu and y.mu in an order that is guaranteed to be
    22  // consistent for both lockTwoPipes(x, y) and lockTwoPipes(y, x), such that
    23  // concurrent calls cannot deadlock.
    24  //
    25  // Preconditions: x != y.
    26  // +checklocksacquire:x.mu
    27  // +checklocksacquire:y.mu
    28  func lockTwoPipes(x, y *Pipe) {
    29  	// Lock the two pipes in order of increasing address.
    30  	if uintptr(unsafe.Pointer(x)) < uintptr(unsafe.Pointer(y)) {
    31  		x.mu.Lock()
    32  		y.mu.Lock()
    33  	} else {
    34  		y.mu.Lock()
    35  		x.mu.Lock()
    36  	}
    37  }