diff options
Diffstat (limited to 'pkg/sentry/kernel/cgroup.go')
| -rw-r--r-- | pkg/sentry/kernel/cgroup.go | 71 |
1 files changed, 55 insertions, 16 deletions
diff --git a/pkg/sentry/kernel/cgroup.go b/pkg/sentry/kernel/cgroup.go index 1f1c63f37..c93ef6ac1 100644 --- a/pkg/sentry/kernel/cgroup.go +++ b/pkg/sentry/kernel/cgroup.go @@ -48,10 +48,6 @@ type CgroupController interface { // attached to. Returned value is valid for the lifetime of the controller. HierarchyID() uint32 - // Filesystem returns the filesystem this controller is attached to. - // Returned value is valid for the lifetime of the controller. - Filesystem() *vfs.Filesystem - // RootCgroup returns the root cgroup for this controller. Returned value is // valid for the lifetime of the controller. RootCgroup() Cgroup @@ -124,6 +120,19 @@ func (h *hierarchy) match(ctypes []CgroupControllerType) bool { return true } +// cgroupFS is the public interface to cgroupfs. This lets the kernel package +// refer to cgroupfs.filesystem methods without directly depending on the +// cgroupfs package, which would lead to a circular dependency. +type cgroupFS interface { + // Returns the vfs.Filesystem for the cgroupfs. + VFSFilesystem() *vfs.Filesystem + + // InitializeHierarchyID sets the hierarchy ID for this filesystem during + // filesystem creation. May only be called before the filesystem is visible + // to the vfs layer. + InitializeHierarchyID(hid uint32) +} + // CgroupRegistry tracks the active set of cgroup controllers on the system. // // +stateify savable @@ -172,7 +181,23 @@ func (r *CgroupRegistry) FindHierarchy(ctypes []CgroupControllerType) *vfs.Files for _, h := range r.hierarchies { if h.match(ctypes) { - h.fs.IncRef() + if !h.fs.TryIncRef() { + // Racing with filesystem destruction, namely h.fs.Release. + // Since we hold r.mu, we know the hierarchy hasn't been + // unregistered yet, but its associated filesystem is tearing + // down. + // + // If we simply indicate the hierarchy wasn't found without + // cleaning up the registry, the caller can race with the + // unregister and find itself temporarily unable to create a new + // hierarchy with a subset of the relevant controllers. + // + // To keep the result of FindHierarchy consistent with the + // uniqueness of controllers enforced by Register, drop the + // dying hierarchy now. The eventual unregister by the FS + // teardown will become a no-op. + return nil + } return h.fs } } @@ -182,31 +207,35 @@ func (r *CgroupRegistry) FindHierarchy(ctypes []CgroupControllerType) *vfs.Files // Register registers the provided set of controllers with the registry as a new // hierarchy. If any controller is already registered, the function returns an -// error without modifying the registry. The hierarchy can be later referenced -// by the returned id. -func (r *CgroupRegistry) Register(cs []CgroupController) (uint32, error) { +// error without modifying the registry. Register sets the hierarchy ID for the +// filesystem on success. +func (r *CgroupRegistry) Register(cs []CgroupController, fs cgroupFS) error { r.mu.Lock() defer r.mu.Unlock() if len(cs) == 0 { - return InvalidCgroupHierarchyID, fmt.Errorf("can't register hierarchy with no controllers") + return fmt.Errorf("can't register hierarchy with no controllers") } for _, c := range cs { if _, ok := r.controllers[c.Type()]; ok { - return InvalidCgroupHierarchyID, fmt.Errorf("controllers may only be mounted on a single hierarchy") + return fmt.Errorf("controllers may only be mounted on a single hierarchy") } } hid, err := r.nextHierarchyID() if err != nil { - return hid, err + return err } + // Must not fail below here, once we publish the hierarchy ID. + + fs.InitializeHierarchyID(hid) + h := hierarchy{ id: hid, controllers: make(map[CgroupControllerType]CgroupController), - fs: cs[0].Filesystem(), + fs: fs.VFSFilesystem(), } for _, c := range cs { n := c.Type() @@ -214,15 +243,20 @@ func (r *CgroupRegistry) Register(cs []CgroupController) (uint32, error) { h.controllers[n] = c } r.hierarchies[hid] = h - return hid, nil + return nil } -// Unregister removes a previously registered hierarchy from the registry. If -// the controller was not previously registered, Unregister is a no-op. +// Unregister removes a previously registered hierarchy from the registry. If no +// such hierarchy is registered, Unregister is a no-op. func (r *CgroupRegistry) Unregister(hid uint32) { r.mu.Lock() - defer r.mu.Unlock() + r.unregisterLocked(hid) + r.mu.Unlock() +} +// Precondition: Caller must hold r.mu. +// +checklocks:r.mu +func (r *CgroupRegistry) unregisterLocked(hid uint32) { if h, ok := r.hierarchies[hid]; ok { for name, _ := range h.controllers { delete(r.controllers, name) @@ -253,6 +287,11 @@ func (r *CgroupRegistry) computeInitialGroups(inherit map[Cgroup]struct{}) map[C for name, ctl := range r.controllers { if _, ok := ctlSet[name]; !ok { cg := ctl.RootCgroup() + // Multiple controllers may share the same hierarchy, so may have + // the same root cgroup. Grab a single ref per hierarchy root. + if _, ok := cgset[cg]; ok { + continue + } cg.IncRef() // Ref transferred to caller. cgset[cg] = struct{}{} } |