diff options
Diffstat (limited to 'pkg/sentry/vfs')
| -rwxr-xr-x | pkg/sentry/vfs/dentry.go | 128 | ||||
| -rwxr-xr-x | pkg/sentry/vfs/mount.go | 319 | ||||
| -rwxr-xr-x | pkg/sentry/vfs/mount_unsafe.go | 60 | ||||
| -rwxr-xr-x | pkg/sentry/vfs/resolving_path.go | 8 | ||||
| -rwxr-xr-x | pkg/sentry/vfs/syscalls.go | 2 | ||||
| -rwxr-xr-x | pkg/sentry/vfs/vfs.go | 11 |
6 files changed, 385 insertions, 143 deletions
diff --git a/pkg/sentry/vfs/dentry.go b/pkg/sentry/vfs/dentry.go index 45912fc58..09ed5a70e 100755 --- a/pkg/sentry/vfs/dentry.go +++ b/pkg/sentry/vfs/dentry.go @@ -16,6 +16,7 @@ package vfs import ( "fmt" + "sync" "sync/atomic" "gvisor.dev/gvisor/pkg/syserror" @@ -50,7 +51,7 @@ import ( // and not inodes. Furthermore, when parties outside the scope of VFS can // rename inodes on such filesystems, VFS generally cannot "follow" the rename, // both due to synchronization issues and because it may not even be able to -// name the destination path; this implies that it would in fact be *incorrect* +// name the destination path; this implies that it would in fact be incorrect // for Dentries to be associated with inodes on such filesystems. Consequently, // operations that are inode operations in Linux are FilesystemImpl methods // and/or FileDescriptionImpl methods in gVisor's VFS. Filesystems that do @@ -84,6 +85,9 @@ type Dentry struct { // mounts is accessed using atomic memory operations. mounts uint32 + // mu synchronizes disowning and mounting over this Dentry. + mu sync.Mutex + // children are child Dentries. children map[string]*Dentry @@ -228,36 +232,48 @@ func (vfs *VirtualFilesystem) PrepareDeleteDentry(mntns *MountNamespace, d *Dent panic("d is already disowned") } } - vfs.mountMu.RLock() - if _, ok := mntns.mountpoints[d]; ok { - vfs.mountMu.RUnlock() + vfs.mountMu.Lock() + if mntns.mountpoints[d] != 0 { + vfs.mountMu.Unlock() return syserror.EBUSY } - // Return with vfs.mountMu locked, which will be unlocked by - // AbortDeleteDentry or CommitDeleteDentry. + d.mu.Lock() + vfs.mountMu.Unlock() + // Return with d.mu locked to block attempts to mount over it; it will be + // unlocked by AbortDeleteDentry or CommitDeleteDentry. return nil } // AbortDeleteDentry must be called after PrepareDeleteDentry if the deletion // fails. -func (vfs *VirtualFilesystem) AbortDeleteDentry() { - vfs.mountMu.RUnlock() +func (vfs *VirtualFilesystem) AbortDeleteDentry(d *Dentry) { + d.mu.Unlock() } // CommitDeleteDentry must be called after the file represented by d is // deleted, and causes d to become disowned. // +// CommitDeleteDentry is a mutator of d and d.Parent(). +// // Preconditions: PrepareDeleteDentry was previously called on d. func (vfs *VirtualFilesystem) CommitDeleteDentry(d *Dentry) { - delete(d.parent.children, d.name) + if d.parent != nil { + delete(d.parent.children, d.name) + } d.setDisowned() - // TODO: lazily unmount mounts at d - vfs.mountMu.RUnlock() + d.mu.Unlock() + if d.isMounted() { + vfs.forgetDisownedMountpoint(d) + } } // DeleteDentry combines PrepareDeleteDentry and CommitDeleteDentry, as // appropriate for in-memory filesystems that don't need to ensure that some // external state change succeeds before committing the deletion. +// +// DeleteDentry is a mutator of d and d.Parent(). +// +// Preconditions: d is a child Dentry. func (vfs *VirtualFilesystem) DeleteDentry(mntns *MountNamespace, d *Dentry) error { if err := vfs.PrepareDeleteDentry(mntns, d); err != nil { return err @@ -266,6 +282,27 @@ func (vfs *VirtualFilesystem) DeleteDentry(mntns *MountNamespace, d *Dentry) err return nil } +// ForceDeleteDentry causes d to become disowned. It should only be used in +// cases where VFS has no ability to stop the deletion (e.g. d represents the +// local state of a file on a remote filesystem on which the file has already +// been deleted). +// +// ForceDeleteDentry is a mutator of d and d.Parent(). +// +// Preconditions: d is a child Dentry. +func (vfs *VirtualFilesystem) ForceDeleteDentry(d *Dentry) { + if checkInvariants { + if d.parent == nil { + panic("d is independent") + } + if d.IsDisowned() { + panic("d is already disowned") + } + } + d.mu.Lock() + vfs.CommitDeleteDentry(d) +} + // PrepareRenameDentry must be called before attempting to rename the file // represented by from. If to is not nil, it represents the file that will be // replaced or exchanged by the rename. If PrepareRenameDentry succeeds, the @@ -291,18 +328,21 @@ func (vfs *VirtualFilesystem) PrepareRenameDentry(mntns *MountNamespace, from, t } } } - vfs.mountMu.RLock() - if _, ok := mntns.mountpoints[from]; ok { - vfs.mountMu.RUnlock() + vfs.mountMu.Lock() + if mntns.mountpoints[from] != 0 { + vfs.mountMu.Unlock() return syserror.EBUSY } if to != nil { - if _, ok := mntns.mountpoints[to]; ok { - vfs.mountMu.RUnlock() + if mntns.mountpoints[to] != 0 { + vfs.mountMu.Unlock() return syserror.EBUSY } + to.mu.Lock() } - // Return with vfs.mountMu locked, which will be unlocked by + from.mu.Lock() + vfs.mountMu.Unlock() + // Return with from.mu and to.mu locked, which will be unlocked by // AbortRenameDentry, CommitRenameReplaceDentry, or // CommitRenameExchangeDentry. return nil @@ -310,38 +350,76 @@ func (vfs *VirtualFilesystem) PrepareRenameDentry(mntns *MountNamespace, from, t // AbortRenameDentry must be called after PrepareRenameDentry if the rename // fails. -func (vfs *VirtualFilesystem) AbortRenameDentry() { - vfs.mountMu.RUnlock() +func (vfs *VirtualFilesystem) AbortRenameDentry(from, to *Dentry) { + from.mu.Unlock() + if to != nil { + to.mu.Unlock() + } } // CommitRenameReplaceDentry must be called after the file represented by from // is renamed without RENAME_EXCHANGE. If to is not nil, it represents the file // that was replaced by from. // +// CommitRenameReplaceDentry is a mutator of from, to, from.Parent(), and +// to.Parent(). +// // Preconditions: PrepareRenameDentry was previously called on from and to. // newParent.Child(newName) == to. func (vfs *VirtualFilesystem) CommitRenameReplaceDentry(from, newParent *Dentry, newName string, to *Dentry) { - if to != nil { - to.setDisowned() - // TODO: lazily unmount mounts at d - } if newParent.children == nil { newParent.children = make(map[string]*Dentry) } newParent.children[newName] = from from.parent = newParent from.name = newName - vfs.mountMu.RUnlock() + from.mu.Unlock() + if to != nil { + to.setDisowned() + to.mu.Unlock() + if to.isMounted() { + vfs.forgetDisownedMountpoint(to) + } + } } // CommitRenameExchangeDentry must be called after the files represented by // from and to are exchanged by rename(RENAME_EXCHANGE). // +// CommitRenameExchangeDentry is a mutator of from, to, from.Parent(), and +// to.Parent(). +// // Preconditions: PrepareRenameDentry was previously called on from and to. func (vfs *VirtualFilesystem) CommitRenameExchangeDentry(from, to *Dentry) { from.parent, to.parent = to.parent, from.parent from.name, to.name = to.name, from.name from.parent.children[from.name] = from to.parent.children[to.name] = to - vfs.mountMu.RUnlock() + from.mu.Unlock() + to.mu.Unlock() +} + +// forgetDisownedMountpoint is called when a mount point is deleted to umount +// all mounts using it in all other mount namespaces. +// +// forgetDisownedMountpoint is analogous to Linux's +// fs/namespace.c:__detach_mounts(). +func (vfs *VirtualFilesystem) forgetDisownedMountpoint(d *Dentry) { + var ( + vdsToDecRef []VirtualDentry + mountsToDecRef []*Mount + ) + vfs.mountMu.Lock() + vfs.mounts.seq.BeginWrite() + for mnt := range vfs.mountpoints[d] { + vdsToDecRef, mountsToDecRef = vfs.umountRecursiveLocked(mnt, &umountRecursiveOptions{}, vdsToDecRef, mountsToDecRef) + } + vfs.mounts.seq.EndWrite() + vfs.mountMu.Unlock() + for _, vd := range vdsToDecRef { + vd.DecRef() + } + for _, mnt := range mountsToDecRef { + mnt.decRef() + } } diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go index 11702f720..198fb8067 100755 --- a/pkg/sentry/vfs/mount.go +++ b/pkg/sentry/vfs/mount.go @@ -38,16 +38,12 @@ import ( // Mount is analogous to Linux's struct mount. (gVisor does not distinguish // between struct mount and struct vfsmount.) type Mount struct { - // The lower 63 bits of refs are a reference count. The MSB of refs is set - // if the Mount has been eagerly unmounted, as by umount(2) without the - // MNT_DETACH flag. refs is accessed using atomic memory operations. - refs int64 - - // The lower 63 bits of writers is the number of calls to - // Mount.CheckBeginWrite() that have not yet been paired with a call to - // Mount.EndWrite(). The MSB of writers is set if MS_RDONLY is in effect. - // writers is accessed using atomic memory operations. - writers int64 + // vfs, fs, and root are immutable. References are held on fs and root. + // + // Invariant: root belongs to fs. + vfs *VirtualFilesystem + fs *Filesystem + root *Dentry // key is protected by VirtualFilesystem.mountMu and // VirtualFilesystem.mounts.seq, and may be nil. References are held on @@ -57,13 +53,29 @@ type Mount struct { // key.parent.fs. key mountKey - // fs, root, and ns are immutable. References are held on fs and root (but - // not ns). - // - // Invariant: root belongs to fs. - fs *Filesystem - root *Dentry - ns *MountNamespace + // ns is the namespace in which this Mount was mounted. ns is protected by + // VirtualFilesystem.mountMu. + ns *MountNamespace + + // The lower 63 bits of refs are a reference count. The MSB of refs is set + // if the Mount has been eagerly umounted, as by umount(2) without the + // MNT_DETACH flag. refs is accessed using atomic memory operations. + refs int64 + + // children is the set of all Mounts for which Mount.key.parent is this + // Mount. children is protected by VirtualFilesystem.mountMu. + children map[*Mount]struct{} + + // umounted is true if VFS.umountRecursiveLocked() has been called on this + // Mount. VirtualFilesystem does not hold a reference on Mounts for which + // umounted is true. umounted is protected by VirtualFilesystem.mountMu. + umounted bool + + // The lower 63 bits of writers is the number of calls to + // Mount.CheckBeginWrite() that have not yet been paired with a call to + // Mount.EndWrite(). The MSB of writers is set if MS_RDONLY is in effect. + // writers is accessed using atomic memory operations. + writers int64 } // A MountNamespace is a collection of Mounts. @@ -73,13 +85,16 @@ type Mount struct { // // MountNamespace is analogous to Linux's struct mnt_namespace. type MountNamespace struct { - refs int64 // accessed using atomic memory operations - // root is the MountNamespace's root mount. root is immutable. root *Mount - // mountpoints contains all Dentries which are mount points in this - // namespace. mountpoints is protected by VirtualFilesystem.mountMu. + // refs is the reference count. refs is accessed using atomic memory + // operations. + refs int64 + + // mountpoints maps all Dentries which are mount points in this namespace + // to the number of Mounts for which they are mount points. mountpoints is + // protected by VirtualFilesystem.mountMu. // // mountpoints is used to determine if a Dentry can be moved or removed // (which requires that the Dentry is not a mount point in the calling @@ -89,7 +104,7 @@ type MountNamespace struct { // MountNamespace; this is required to ensure that // VFS.PrepareDeleteDentry() and VFS.PrepareRemoveDentry() operate // correctly on unreferenced MountNamespaces. - mountpoints map[*Dentry]struct{} + mountpoints map[*Dentry]uint32 } // NewMountNamespace returns a new mount namespace with a root filesystem @@ -106,9 +121,10 @@ func (vfs *VirtualFilesystem) NewMountNamespace(ctx context.Context, creds *auth } mntns := &MountNamespace{ refs: 1, - mountpoints: make(map[*Dentry]struct{}), + mountpoints: make(map[*Dentry]uint32), } mntns.root = &Mount{ + vfs: vfs, fs: fs, root: root, ns: mntns, @@ -136,8 +152,10 @@ func (vfs *VirtualFilesystem) NewMount(ctx context.Context, creds *auth.Credenti return err } vfs.mountMu.Lock() + vd.dentry.mu.Lock() for { if vd.dentry.IsDisowned() { + vd.dentry.mu.Unlock() vfs.mountMu.Unlock() vd.DecRef() root.decRef(fs) @@ -153,36 +171,208 @@ func (vfs *VirtualFilesystem) NewMount(ctx context.Context, creds *auth.Credenti if nextmnt == nil { break } - nextmnt.incRef() + // It's possible that nextmnt has been umounted but not disconnected, + // in which case vfs no longer holds a reference on it, and the last + // reference may be concurrently dropped even though we're holding + // vfs.mountMu. + if !nextmnt.tryIncMountedRef() { + break + } + // This can't fail since we're holding vfs.mountMu. nextmnt.root.incRef(nextmnt.fs) + vd.dentry.mu.Unlock() vd.DecRef() vd = VirtualDentry{ mount: nextmnt, dentry: nextmnt.root, } + vd.dentry.mu.Lock() } // TODO: Linux requires that either both the mount point and the mount root // are directories, or neither are, and returns ENOTDIR if this is not the // case. mntns := vd.mount.ns mnt := &Mount{ + vfs: vfs, fs: fs, root: root, ns: mntns, refs: 1, } - mnt.storeKey(vd.mount, vd.dentry) + vfs.mounts.seq.BeginWrite() + vfs.connectLocked(mnt, vd, mntns) + vfs.mounts.seq.EndWrite() + vd.dentry.mu.Unlock() + vfs.mountMu.Unlock() + return nil +} + +type umountRecursiveOptions struct { + // If eager is true, ensure that future calls to Mount.tryIncMountedRef() + // on umounted mounts fail. + // + // eager is analogous to Linux's UMOUNT_SYNC. + eager bool + + // If disconnectHierarchy is true, Mounts that are umounted hierarchically + // should be disconnected from their parents. (Mounts whose parents are not + // umounted, which in most cases means the Mount passed to the initial call + // to umountRecursiveLocked, are unconditionally disconnected for + // consistency with Linux.) + // + // disconnectHierarchy is analogous to Linux's !UMOUNT_CONNECTED. + disconnectHierarchy bool +} + +// umountRecursiveLocked marks mnt and its descendants as umounted. It does not +// release mount or dentry references; instead, it appends VirtualDentries and +// Mounts on which references must be dropped to vdsToDecRef and mountsToDecRef +// respectively, and returns updated slices. (This is necessary because +// filesystem locks possibly taken by DentryImpl.DecRef() may precede +// vfs.mountMu in the lock order, and Mount.decRef() may lock vfs.mountMu.) +// +// umountRecursiveLocked is analogous to Linux's fs/namespace.c:umount_tree(). +// +// Preconditions: vfs.mountMu must be locked. vfs.mounts.seq must be in a +// writer critical section. +func (vfs *VirtualFilesystem) umountRecursiveLocked(mnt *Mount, opts *umountRecursiveOptions, vdsToDecRef []VirtualDentry, mountsToDecRef []*Mount) ([]VirtualDentry, []*Mount) { + if !mnt.umounted { + mnt.umounted = true + mountsToDecRef = append(mountsToDecRef, mnt) + if parent := mnt.parent(); parent != nil && (opts.disconnectHierarchy || !parent.umounted) { + vdsToDecRef = append(vdsToDecRef, vfs.disconnectLocked(mnt)) + } + } + if opts.eager { + for { + refs := atomic.LoadInt64(&mnt.refs) + if refs < 0 { + break + } + if atomic.CompareAndSwapInt64(&mnt.refs, refs, refs|math.MinInt64) { + break + } + } + } + for child := range mnt.children { + vdsToDecRef, mountsToDecRef = vfs.umountRecursiveLocked(child, opts, vdsToDecRef, mountsToDecRef) + } + return vdsToDecRef, mountsToDecRef +} + +// connectLocked makes vd the mount parent/point for mnt. It consumes +// references held by vd. +// +// Preconditions: vfs.mountMu must be locked. vfs.mounts.seq must be in a +// writer critical section. d.mu must be locked. mnt.parent() == nil. +func (vfs *VirtualFilesystem) connectLocked(mnt *Mount, vd VirtualDentry, mntns *MountNamespace) { + mnt.storeKey(vd) + if vd.mount.children == nil { + vd.mount.children = make(map[*Mount]struct{}) + } + vd.mount.children[mnt] = struct{}{} atomic.AddUint32(&vd.dentry.mounts, 1) - mntns.mountpoints[vd.dentry] = struct{}{} + mntns.mountpoints[vd.dentry]++ + vfs.mounts.insertSeqed(mnt) vfsmpmounts, ok := vfs.mountpoints[vd.dentry] if !ok { vfsmpmounts = make(map[*Mount]struct{}) vfs.mountpoints[vd.dentry] = vfsmpmounts } vfsmpmounts[mnt] = struct{}{} - vfs.mounts.Insert(mnt) - vfs.mountMu.Unlock() - return nil +} + +// disconnectLocked makes vd have no mount parent/point and returns its old +// mount parent/point with a reference held. +// +// Preconditions: vfs.mountMu must be locked. vfs.mounts.seq must be in a +// writer critical section. mnt.parent() != nil. +func (vfs *VirtualFilesystem) disconnectLocked(mnt *Mount) VirtualDentry { + vd := mnt.loadKey() + mnt.storeKey(VirtualDentry{}) + delete(vd.mount.children, mnt) + atomic.AddUint32(&vd.dentry.mounts, math.MaxUint32) // -1 + mnt.ns.mountpoints[vd.dentry]-- + if mnt.ns.mountpoints[vd.dentry] == 0 { + delete(mnt.ns.mountpoints, vd.dentry) + } + vfs.mounts.removeSeqed(mnt) + vfsmpmounts := vfs.mountpoints[vd.dentry] + delete(vfsmpmounts, mnt) + if len(vfsmpmounts) == 0 { + delete(vfs.mountpoints, vd.dentry) + } + return vd +} + +// tryIncMountedRef increments mnt's reference count and returns true. If mnt's +// reference count is already zero, or has been eagerly umounted, +// tryIncMountedRef does nothing and returns false. +// +// tryIncMountedRef does not require that a reference is held on mnt. +func (mnt *Mount) tryIncMountedRef() bool { + for { + refs := atomic.LoadInt64(&mnt.refs) + if refs <= 0 { // refs < 0 => MSB set => eagerly unmounted + return false + } + if atomic.CompareAndSwapInt64(&mnt.refs, refs, refs+1) { + return true + } + } +} + +func (mnt *Mount) incRef() { + // In general, negative values for mnt.refs are valid because the MSB is + // the eager-unmount bit. + atomic.AddInt64(&mnt.refs, 1) +} + +func (mnt *Mount) decRef() { + refs := atomic.AddInt64(&mnt.refs, -1) + if refs&^math.MinInt64 == 0 { // mask out MSB + var vd VirtualDentry + if mnt.parent() != nil { + mnt.vfs.mountMu.Lock() + mnt.vfs.mounts.seq.BeginWrite() + vd = mnt.vfs.disconnectLocked(mnt) + mnt.vfs.mounts.seq.EndWrite() + mnt.vfs.mountMu.Unlock() + } + mnt.root.decRef(mnt.fs) + mnt.fs.decRef() + if vd.Ok() { + vd.DecRef() + } + } +} + +// IncRef increments mntns' reference count. +func (mntns *MountNamespace) IncRef() { + if atomic.AddInt64(&mntns.refs, 1) <= 1 { + panic("MountNamespace.IncRef() called without holding a reference") + } +} + +// DecRef decrements mntns' reference count. +func (mntns *MountNamespace) DecRef(vfs *VirtualFilesystem) { + if refs := atomic.AddInt64(&mntns.refs, -1); refs == 0 { + vfs.mountMu.Lock() + vfs.mounts.seq.BeginWrite() + vdsToDecRef, mountsToDecRef := vfs.umountRecursiveLocked(mntns.root, &umountRecursiveOptions{ + disconnectHierarchy: true, + }, nil, nil) + vfs.mounts.seq.EndWrite() + vfs.mountMu.Unlock() + for _, vd := range vdsToDecRef { + vd.DecRef() + } + for _, mnt := range mountsToDecRef { + mnt.decRef() + } + } else if refs < 0 { + panic("MountNamespace.DecRef() called without holding a reference") + } } // getMountAt returns the last Mount in the stack mounted at (mnt, d). It takes @@ -231,12 +421,12 @@ retryFirst: } // getMountpointAt returns the mount point for the stack of Mounts including -// mnt. It takes a reference on the returned Mount and Dentry. If no such mount +// mnt. It takes a reference on the returned VirtualDentry. If no such mount // point exists (i.e. mnt is a root mount), getMountpointAt returns (nil, nil). // // Preconditions: References are held on mnt and root. vfsroot is not (mnt, // mnt.root). -func (vfs *VirtualFilesystem) getMountpointAt(mnt *Mount, vfsroot VirtualDentry) (*Mount, *Dentry) { +func (vfs *VirtualFilesystem) getMountpointAt(mnt *Mount, vfsroot VirtualDentry) VirtualDentry { // The first mount is special-cased: // // - The caller must have already checked mnt against vfsroot. @@ -246,12 +436,12 @@ func (vfs *VirtualFilesystem) getMountpointAt(mnt *Mount, vfsroot VirtualDentry) // - We don't drop the caller's reference on mnt. retryFirst: epoch := vfs.mounts.seq.BeginRead() - parent, point := mnt.loadKey() + parent, point := mnt.parent(), mnt.point() if !vfs.mounts.seq.ReadOk(epoch) { goto retryFirst } if parent == nil { - return nil, nil + return VirtualDentry{} } if !parent.tryIncMountedRef() { // Raced with umount. @@ -263,6 +453,11 @@ retryFirst: parent.decRef() goto retryFirst } + if !vfs.mounts.seq.ReadOk(epoch) { + point.decRef(parent.fs) + parent.decRef() + goto retryFirst + } mnt = parent d := point for { @@ -274,7 +469,7 @@ retryFirst: } retryNotFirst: epoch := vfs.mounts.seq.BeginRead() - parent, point := mnt.loadKey() + parent, point := mnt.parent(), mnt.point() if !vfs.mounts.seq.ReadOk(epoch) { goto retryNotFirst } @@ -301,43 +496,7 @@ retryFirst: mnt = parent d = point } - return mnt, d -} - -// tryIncMountedRef increments mnt's reference count and returns true. If mnt's -// reference count is already zero, or has been eagerly unmounted, -// tryIncMountedRef does nothing and returns false. -// -// tryIncMountedRef does not require that a reference is held on mnt. -func (mnt *Mount) tryIncMountedRef() bool { - for { - refs := atomic.LoadInt64(&mnt.refs) - if refs <= 0 { // refs < 0 => MSB set => eagerly unmounted - return false - } - if atomic.CompareAndSwapInt64(&mnt.refs, refs, refs+1) { - return true - } - } -} - -func (mnt *Mount) incRef() { - // In general, negative values for mnt.refs are valid because the MSB is - // the eager-unmount bit. - atomic.AddInt64(&mnt.refs, 1) -} - -func (mnt *Mount) decRef() { - refs := atomic.AddInt64(&mnt.refs, -1) - if refs&^math.MinInt64 == 0 { // mask out MSB - parent, point := mnt.loadKey() - if point != nil { - point.decRef(parent.fs) - parent.decRef() - } - mnt.root.decRef(mnt.fs) - mnt.fs.decRef() - } + return VirtualDentry{mnt, d} } // CheckBeginWrite increments the counter of in-progress write operations on @@ -360,7 +519,7 @@ func (mnt *Mount) EndWrite() { atomic.AddInt64(&mnt.writers, -1) } -// Preconditions: VirtualFilesystem.mountMu must be locked for writing. +// Preconditions: VirtualFilesystem.mountMu must be locked. func (mnt *Mount) setReadOnlyLocked(ro bool) error { if oldRO := atomic.LoadInt64(&mnt.writers) < 0; oldRO == ro { return nil @@ -383,22 +542,6 @@ func (mnt *Mount) Filesystem() *Filesystem { return mnt.fs } -// IncRef increments mntns' reference count. -func (mntns *MountNamespace) IncRef() { - if atomic.AddInt64(&mntns.refs, 1) <= 1 { - panic("MountNamespace.IncRef() called without holding a reference") - } -} - -// DecRef decrements mntns' reference count. -func (mntns *MountNamespace) DecRef() { - if refs := atomic.AddInt64(&mntns.refs, 0); refs == 0 { - // TODO: unmount mntns.root - } else if refs < 0 { - panic("MountNamespace.DecRef() called without holding a reference") - } -} - // Root returns mntns' root. A reference is taken on the returned // VirtualDentry. func (mntns *MountNamespace) Root() VirtualDentry { diff --git a/pkg/sentry/vfs/mount_unsafe.go b/pkg/sentry/vfs/mount_unsafe.go index c98b42f91..ab13fa461 100755 --- a/pkg/sentry/vfs/mount_unsafe.go +++ b/pkg/sentry/vfs/mount_unsafe.go @@ -38,16 +38,6 @@ type mountKey struct { point unsafe.Pointer // *Dentry } -// Invariant: mnt.key's fields are nil. parent and point are non-nil. -func (mnt *Mount) storeKey(parent *Mount, point *Dentry) { - atomic.StorePointer(&mnt.key.parent, unsafe.Pointer(parent)) - atomic.StorePointer(&mnt.key.point, unsafe.Pointer(point)) -} - -func (mnt *Mount) loadKey() (*Mount, *Dentry) { - return (*Mount)(atomic.LoadPointer(&mnt.key.parent)), (*Dentry)(atomic.LoadPointer(&mnt.key.point)) -} - func (mnt *Mount) parent() *Mount { return (*Mount)(atomic.LoadPointer(&mnt.key.parent)) } @@ -56,6 +46,19 @@ func (mnt *Mount) point() *Dentry { return (*Dentry)(atomic.LoadPointer(&mnt.key.point)) } +func (mnt *Mount) loadKey() VirtualDentry { + return VirtualDentry{ + mount: mnt.parent(), + dentry: mnt.point(), + } +} + +// Invariant: mnt.key.parent == nil. vd.Ok(). +func (mnt *Mount) storeKey(vd VirtualDentry) { + atomic.StorePointer(&mnt.key.parent, unsafe.Pointer(vd.mount)) + atomic.StorePointer(&mnt.key.point, unsafe.Pointer(vd.dentry)) +} + // mountTable maps (mount parent, mount point) pairs to mounts. It supports // efficient concurrent lookup, even in the presence of concurrent mutators // (provided mutation is sufficiently uncommon). @@ -201,9 +204,19 @@ loop: // Insert inserts the given mount into mt. // -// Preconditions: There are no concurrent mutators of mt. mt must not already -// contain a Mount with the same mount point and parent. +// Preconditions: mt must not already contain a Mount with the same mount point +// and parent. func (mt *mountTable) Insert(mount *Mount) { + mt.seq.BeginWrite() + mt.insertSeqed(mount) + mt.seq.EndWrite() +} + +// insertSeqed inserts the given mount into mt. +// +// Preconditions: mt.seq must be in a writer critical section. mt must not +// already contain a Mount with the same mount point and parent. +func (mt *mountTable) insertSeqed(mount *Mount) { hash := memhash(unsafe.Pointer(&mount.key), uintptr(mt.seed), mountKeyBytes) // We're under the maximum load factor if: @@ -215,10 +228,8 @@ func (mt *mountTable) Insert(mount *Mount) { tcap := uintptr(1) << order if ((tlen + 1) * mtMaxLoadDen) <= (uint64(mtMaxLoadNum) << order) { // Atomically insert the new element into the table. - mt.seq.BeginWrite() atomic.AddUint64(&mt.size, mtSizeLenOne) mtInsertLocked(mt.slots, tcap, unsafe.Pointer(mount), hash) - mt.seq.EndWrite() return } @@ -241,8 +252,6 @@ func (mt *mountTable) Insert(mount *Mount) { for { oldSlot := (*mountSlot)(oldCur) if oldSlot.value != nil { - // Don't need to lock mt.seq yet since newSlots isn't visible - // to readers. mtInsertLocked(newSlots, newCap, oldSlot.value, oldSlot.hash) } if oldCur == oldLast { @@ -252,11 +261,9 @@ func (mt *mountTable) Insert(mount *Mount) { } // Insert the new element into the new table. mtInsertLocked(newSlots, newCap, unsafe.Pointer(mount), hash) - // Atomically switch to the new table. - mt.seq.BeginWrite() + // Switch to the new table. atomic.AddUint64(&mt.size, mtSizeLenOne|mtSizeOrderOne) atomic.StorePointer(&mt.slots, newSlots) - mt.seq.EndWrite() } // Preconditions: There are no concurrent mutators of the table (slots, cap). @@ -294,9 +301,18 @@ func mtInsertLocked(slots unsafe.Pointer, cap uintptr, value unsafe.Pointer, has // Remove removes the given mount from mt. // -// Preconditions: There are no concurrent mutators of mt. mt must contain -// mount. +// Preconditions: mt must contain mount. func (mt *mountTable) Remove(mount *Mount) { + mt.seq.BeginWrite() + mt.removeSeqed(mount) + mt.seq.EndWrite() +} + +// removeSeqed removes the given mount from mt. +// +// Preconditions: mt.seq must be in a writer critical section. mt must contain +// mount. +func (mt *mountTable) removeSeqed(mount *Mount) { hash := memhash(unsafe.Pointer(&mount.key), uintptr(mt.seed), mountKeyBytes) tcap := uintptr(1) << (mt.size & mtSizeOrderMask) mask := tcap - 1 @@ -311,7 +327,6 @@ func (mt *mountTable) Remove(mount *Mount) { // backward until we either find an empty slot, or an element that // is already in its first-probed slot. (This is backward shift // deletion.) - mt.seq.BeginWrite() for { nextOff := (off + mountSlotBytes) & offmask nextSlot := (*mountSlot)(unsafe.Pointer(uintptr(slots) + nextOff)) @@ -330,7 +345,6 @@ func (mt *mountTable) Remove(mount *Mount) { } atomic.StorePointer(&slot.value, nil) atomic.AddUint64(&mt.size, mtSizeLenNegOne) - mt.seq.EndWrite() return } if checkInvariants && slotValue == nil { diff --git a/pkg/sentry/vfs/resolving_path.go b/pkg/sentry/vfs/resolving_path.go index 8d05c8583..61bce6426 100755 --- a/pkg/sentry/vfs/resolving_path.go +++ b/pkg/sentry/vfs/resolving_path.go @@ -269,11 +269,11 @@ func (rp *ResolvingPath) ResolveParent(d *Dentry) (*Dentry, error) { parent = d } else if d == rp.mount.root { // At mount root ... - mnt, mntpt := rp.vfs.getMountpointAt(rp.mount, rp.root) - if mnt != nil { + vd := rp.vfs.getMountpointAt(rp.mount, rp.root) + if vd.Ok() { // ... of non-root mount. - rp.nextMount = mnt - rp.nextStart = mntpt + rp.nextMount = vd.mount + rp.nextStart = vd.dentry return nil, resolveMountRootError{} } // ... of root mount. diff --git a/pkg/sentry/vfs/syscalls.go b/pkg/sentry/vfs/syscalls.go index abde0feaa..49952b2cc 100755 --- a/pkg/sentry/vfs/syscalls.go +++ b/pkg/sentry/vfs/syscalls.go @@ -230,6 +230,8 @@ func (fd *FileDescription) SetStatusFlags(ctx context.Context, flags uint32) err // // - VFS.SymlinkAt() // +// - VFS.UmountAt() +// // - VFS.UnlinkAt() // // - FileDescription.(almost everything) diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go index 4a8a69540..88e865d86 100755 --- a/pkg/sentry/vfs/vfs.go +++ b/pkg/sentry/vfs/vfs.go @@ -16,9 +16,14 @@ // // Lock order: // -// Filesystem implementation locks +// FilesystemImpl/FileDescriptionImpl locks // VirtualFilesystem.mountMu +// Dentry.mu +// Locks acquired by FilesystemImpls between Prepare{Delete,Rename}Dentry and Commit{Delete,Rename*}Dentry // VirtualFilesystem.fsTypesMu +// +// Locking Dentry.mu in multiple Dentries requires holding +// VirtualFilesystem.mountMu. package vfs import ( @@ -33,7 +38,7 @@ type VirtualFilesystem struct { // mountMu serializes mount mutations. // // mountMu is analogous to Linux's namespace_sem. - mountMu sync.RWMutex + mountMu sync.Mutex // mounts maps (mount parent, mount point) pairs to mounts. (Since mounts // are uniquely namespaced, including mount parent in the key correctly @@ -52,7 +57,7 @@ type VirtualFilesystem struct { // mountpoints maps mount points to mounts at those points in all // namespaces. mountpoints is protected by mountMu. // - // mountpoints is used to find mounts that must be unmounted due to + // mountpoints is used to find mounts that must be umounted due to // removal of a mount point Dentry from another mount namespace. ("A file // or directory that is a mount point in one namespace that is not a mount // point in another namespace, may be renamed, unlinked, or removed |