Le 09/09/2022 à 02:51, Suren Baghdasaryan a écrit : > On Tue, Sep 6, 2022 at 8:35 AM Laurent Dufour <ldufour@xxxxxxxxxxxxx> 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@xxxxxxxxxx> >>> --- >>> 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@xxxxxxxxxxx. >>
