On Tue 20-03-18 14:35:28, Mike Kravetz wrote:
> On 03/20/2018 02:26 PM, Mike Kravetz wrote:
> > Thanks Laurent!
> >
> > This bug was introduced by 31383c6865a5. Dan's changes for 31383c6865a5
> > seem pretty straight forward. It simply replaces an explicit check when
> > splitting a vma to a new vm_ops split callout. Unfortunately, mappings
> > created via shmget/shmat have their vm_ops replaced. Therefore, this
> > split callout is never made.
> >
> > The shm vm_ops do indirectly call the original vm_ops routines as needed.
> > Therefore, I would suggest a patch something like the following instead.
> > If we move forward with the patch, we should include Laurent's BUG output
> > and perhaps test program in the commit message.
>
> Sorry, patch in previous mail was a mess
>
> >From 7a19414319c7937fd2757c27f936258f16c1f61d Mon Sep 17 00:00:00 2001
> From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Date: Tue, 20 Mar 2018 13:56:57 -0700
> Subject: [PATCH] shm: add split function to shm_vm_ops
>
> The split function was added to vm_operations_struct to determine
> if a mapping can be split. This was mostly for device-dax and
> hugetlbfs mappings which have specific alignment constraints.
>
> mappings initiated via shmget/shmat have their original vm_ops
> overwritten with shm_vm_ops. shm_vm_ops functions will call back
> to the original vm_ops if needed. Add such a split function.
>
> Fixes: 31383c6865a5 ("mm, hugetlbfs: introduce ->split() to vm_operations_struct)
> Reported by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Yes this looks much better than the original hugetlb specific code in
the generic vma code.
Please add the original VM_BUG_ON report to the changelog
Cc: stable
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> ipc/shm.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 7acda23430aa..50e88fc060b1 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -386,6 +386,17 @@ static int shm_fault(struct vm_fault *vmf)
> return sfd->vm_ops->fault(vmf);
> }
>
> +static int shm_split(struct vm_area_struct *vma, unsigned long addr)
> +{
> + struct file *file = vma->vm_file;
> + struct shm_file_data *sfd = shm_file_data(file);
> +
> + if (sfd->vm_ops && sfd->vm_ops->split)
> + return sfd->vm_ops->split(vma, addr);
> +
> + return 0;
> +}
> +
> #ifdef CONFIG_NUMA
> static int shm_set_policy(struct vm_area_struct *vma, struct mempolicy *new)
> {
> @@ -510,6 +521,7 @@ static const struct vm_operations_struct shm_vm_ops = {
> .open = shm_open, /* callback for a new vm-area open */
> .close = shm_close, /* callback for when the vm-area is released */
> .fault = shm_fault,
> + .split = shm_split,
> #if defined(CONFIG_NUMA)
> .set_policy = shm_set_policy,
> .get_policy = shm_get_policy,
> --
> 2.13.6
--
Michal Hocko
SUSE Labs
