| Message ID | 20220901173516.702122-11-surenb@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | per-VMA locks proposal | expand |
Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit : > vma_adjust modifies a VMA and possibly its neighbors. Mark them as locked > before making the modifications. > > Signed-off-by: Suren Baghdasaryan <surenb@google.com> > --- > mm/mmap.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index f89c9b058105..ed58cf0689b2 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -710,6 +710,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, > long adjust_next = 0; > int remove_next = 0; > > + vma_mark_locked(vma); > + if (next) > + vma_mark_locked(next); > + I was wondering if the VMAs insert and expand should be locked too. For expand, I can't see any valid reason, but for insert, I'm puzzled. I would think that it is better to lock the VMA to be inserted but I can't really justify that. It may be nice to detail why this is not need to lock insert and expand here. > if (next && !insert) { > struct vm_area_struct *exporter = NULL, *importer = NULL; > > @@ -754,8 +758,11 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, > * If next doesn't have anon_vma, import from vma after > * next, if the vma overlaps with it. > */ > - if (remove_next == 2 && !next->anon_vma) > + if (remove_next == 2 && !next->anon_vma) { > exporter = next->vm_next; > + if (exporter) > + vma_mark_locked(exporter); > + } > > } else if (end > next->vm_start) { > /* > @@ -931,6 +938,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, > * "vma->vm_next" gap must be updated. > */ > next = vma->vm_next; > + if (next) > + vma_mark_locked(next); > } else { > /* > * For the scope of the comment "next" and
On Tue, Sep 6, 2022 at 8:35 AM Laurent Dufour <ldufour@linux.ibm.com> wrote: > > Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit : > > vma_adjust modifies a VMA and possibly its neighbors. Mark them as locked > > before making the modifications. > > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com> > > --- > > mm/mmap.c | 11 ++++++++++- > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index f89c9b058105..ed58cf0689b2 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -710,6 +710,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, > > long adjust_next = 0; > > int remove_next = 0; > > > > + vma_mark_locked(vma); > > + if (next) > > + vma_mark_locked(next); > > + > > I was wondering if the VMAs insert and expand should be locked too. > > For expand, I can't see any valid reason, but for insert, I'm puzzled. > I would think that it is better to lock the VMA to be inserted but I can't > really justify that. > > It may be nice to detail why this is not need to lock insert and expand here. 'expand' is always locked before it's passed to __vma_adjust() by vma_merge(). It has to be locked before we decide "Can it merge with the predecessor?" here https://elixir.bootlin.com/linux/latest/source/mm/mmap.c#L1201 because a change in VMA can affect that decision. I spent many hours tracking the issue caused by not locking the VMA before making this decision. It might be good to add a comment about this... AFAIKT 'insert' is only used by __split_vma() and it's always a brand new VMA which is not yet linked into mm->mmap. Any reason __vma_adjust() should lock it? > > > if (next && !insert) { > > struct vm_area_struct *exporter = NULL, *importer = NULL; > > > > @@ -754,8 +758,11 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, > > * If next doesn't have anon_vma, import from vma after > > * next, if the vma overlaps with it. > > */ > > - if (remove_next == 2 && !next->anon_vma) > > + if (remove_next == 2 && !next->anon_vma) { > > exporter = next->vm_next; > > + if (exporter) > > + vma_mark_locked(exporter); > > + } > > > > } else if (end > next->vm_start) { > > /* > > @@ -931,6 +938,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, > > * "vma->vm_next" gap must be updated. > > */ > > next = vma->vm_next; > > + if (next) > > + vma_mark_locked(next); > > } else { > > /* > > * For the scope of the comment "next" and > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >
Le 09/09/2022 à 02:51, Suren Baghdasaryan a écrit : > On Tue, Sep 6, 2022 at 8:35 AM Laurent Dufour <ldufour@linux.ibm.com> wrote: >> >> Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit : >>> vma_adjust modifies a VMA and possibly its neighbors. Mark them as locked >>> before making the modifications. >>> >>> Signed-off-by: Suren Baghdasaryan <surenb@google.com> >>> --- >>> mm/mmap.c | 11 ++++++++++- >>> 1 file changed, 10 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/mmap.c b/mm/mmap.c >>> index f89c9b058105..ed58cf0689b2 100644 >>> --- a/mm/mmap.c >>> +++ b/mm/mmap.c >>> @@ -710,6 +710,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, >>> long adjust_next = 0; >>> int remove_next = 0; >>> >>> + vma_mark_locked(vma); >>> + if (next) >>> + vma_mark_locked(next); >>> + >> >> I was wondering if the VMAs insert and expand should be locked too. >> >> For expand, I can't see any valid reason, but for insert, I'm puzzled. >> I would think that it is better to lock the VMA to be inserted but I can't >> really justify that. >> >> It may be nice to detail why this is not need to lock insert and expand here. > > 'expand' is always locked before it's passed to __vma_adjust() by > vma_merge(). It has to be locked before we decide "Can it merge with > the predecessor?" here > https://elixir.bootlin.com/linux/latest/source/mm/mmap.c#L1201 because > a change in VMA can affect that decision. I spent many hours tracking > the issue caused by not locking the VMA before making this decision. > It might be good to add a comment about this... > > AFAIKT 'insert' is only used by __split_vma() and it's always a brand > new VMA which is not yet linked into mm->mmap. Any reason > __vma_adjust() should lock it? No, I think that's good this way. > >> >>> if (next && !insert) { >>> struct vm_area_struct *exporter = NULL, *importer = NULL; >>> >>> @@ -754,8 +758,11 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, >>> * If next doesn't have anon_vma, import from vma after >>> * next, if the vma overlaps with it. >>> */ >>> - if (remove_next == 2 && !next->anon_vma) >>> + if (remove_next == 2 && !next->anon_vma) { >>> exporter = next->vm_next; >>> + if (exporter) >>> + vma_mark_locked(exporter); >>> + } >>> >>> } else if (end > next->vm_start) { >>> /* >>> @@ -931,6 +938,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, >>> * "vma->vm_next" gap must be updated. >>> */ >>> next = vma->vm_next; >>> + if (next) >>> + vma_mark_locked(next); >>> } else { >>> /* >>> * For the scope of the comment "next" and >> >> -- >> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >>
diff --git a/mm/mmap.c b/mm/mmap.c index f89c9b058105..ed58cf0689b2 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -710,6 +710,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, long adjust_next = 0; int remove_next = 0; + vma_mark_locked(vma); + if (next) + vma_mark_locked(next); + if (next && !insert) { struct vm_area_struct *exporter = NULL, *importer = NULL; @@ -754,8 +758,11 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, * If next doesn't have anon_vma, import from vma after * next, if the vma overlaps with it. */ - if (remove_next == 2 && !next->anon_vma) + if (remove_next == 2 && !next->anon_vma) { exporter = next->vm_next; + if (exporter) + vma_mark_locked(exporter); + } } else if (end > next->vm_start) { /* @@ -931,6 +938,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, * "vma->vm_next" gap must be updated. */ next = vma->vm_next; + if (next) + vma_mark_locked(next); } else { /* * For the scope of the comment "next" and
vma_adjust modifies a VMA and possibly its neighbors. Mark them as locked before making the modifications. Signed-off-by: Suren Baghdasaryan <surenb@google.com> --- mm/mmap.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)