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>
---
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
