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Rahat MahmoodandgVisor bot
4191bf4959
Otherwise we get circular locking with various filesystem locks if the dropped ref is the final ref. Mapping identities are typically file descriptions on various filesystems, which in turn call mm functions under the respective filesystem locks. PiperOrigin-RevId: 442919016
80 lines
2.3 KiB
Go
80 lines
2.3 KiB
Go
// Copyright 2018 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package mm
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import (
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"gvisor.dev/gvisor/pkg/context"
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"gvisor.dev/gvisor/pkg/errors/linuxerr"
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"gvisor.dev/gvisor/pkg/hostarch"
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"gvisor.dev/gvisor/pkg/sentry/kernel/shm"
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"gvisor.dev/gvisor/pkg/sentry/memmap"
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)
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// DetachShm unmaps a sysv shared memory segment.
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func (mm *MemoryManager) DetachShm(ctx context.Context, addr hostarch.Addr) error {
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if addr != addr.RoundDown() {
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// "... shmaddr is not aligned on a page boundary." - man shmdt(2)
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return linuxerr.EINVAL
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}
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var detached *shm.Shm
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var vgap vmaGapIterator
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var droppedIDs []memmap.MappingIdentity
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// This must run after mm.mappingMu.Unlock().
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defer func() {
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for _, id := range droppedIDs {
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id.DecRef(ctx)
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}
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}()
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mm.mappingMu.Lock()
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defer mm.mappingMu.Unlock()
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// Find and remove the first vma containing an address >= addr that maps a
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// segment originally attached at addr.
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vseg := mm.vmas.LowerBoundSegment(addr)
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for vseg.Ok() {
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vma := vseg.ValuePtr()
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if shm, ok := vma.mappable.(*shm.Shm); ok && vseg.Start() >= addr && uint64(vseg.Start()-addr) == vma.off {
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detached = shm
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vgap, droppedIDs = mm.unmapLocked(ctx, vseg.Range(), droppedIDs)
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vseg = vgap.NextSegment()
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break
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} else {
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vseg = vseg.NextSegment()
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}
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}
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if detached == nil {
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// There is no shared memory segment attached at addr.
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return linuxerr.EINVAL
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}
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// Remove all vmas that could have been created by the same attach.
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end := addr + hostarch.Addr(detached.EffectiveSize())
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for vseg.Ok() && vseg.End() <= end {
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vma := vseg.ValuePtr()
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if vma.mappable == detached && uint64(vseg.Start()-addr) == vma.off {
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vgap, droppedIDs = mm.unmapLocked(ctx, vseg.Range(), droppedIDs)
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vseg = vgap.NextSegment()
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} else {
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vseg = vseg.NextSegment()
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}
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}
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return nil
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}
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