[Devel] [PATCH RHEL7 COMMIT] pfcache: don't inherit vm_private_data on split and copy

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-862.11.6.vz7.71.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-862.11.6.vz7.71.15
------>
commit 60e756297e4dc2adec589c89bcfdc17b86c2ced2
Author: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Date:   Thu Sep 27 11:53:50 2018 +0300

    pfcache: don't inherit vm_private_data on split and copy
    
    BUG_ON in synchronize_mapping_faults_vma triggered again, now we have:
    
    crash> p *((struct vm_area_struct *) 0xffff88061dc890a0) -x
      vm_start = 0x7fa0b794a000,
      vm_prev = 0xffff8801194fe0e0,
      vm_flags = 0x8100073,
      vm_private_data2 = 0xffff8801194fe0e0,
    
    Our vma has vm_private_data2 link set to different vma:
    
    crash> p *((struct vm_area_struct *) 0xffff8801194fe0e0) -x
      vm_end = 0x7fa0b794a000,
      vm_next = 0xffff88061dc890a0,
      vm_flags = 0x8100071,
    
    These two are neighbours and VM_WRITE flag is only set for the first
    mount, looks like we got such vmas from split_vma.
    
    So we need to reset vm_private_data2 everywhere we copy the contents of
    vm_area_struct to a new entry. Found three more places searching after
    "kmem_cache_alloc(vm_area_cachep, GFP_KERNEL)".
    
    https://jira.sw.ru/browse/PSBM-88809
    
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    Acked-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 mm/mmap.c  | 3 +++
 mm/nommu.c | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index e316e1e6eabb..bcb6a9dbcc28 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2706,6 +2706,8 @@ static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 		new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
 	}
 
+	new->vm_private_data2 = NULL;
+
 	pol = mpol_dup(vma_policy(vma));
 	if (IS_ERR(pol)) {
 		err = PTR_ERR(pol);
@@ -3260,6 +3262,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 			new_vma->vm_start = addr;
 			new_vma->vm_end = addr + len;
 			new_vma->vm_pgoff = pgoff;
+			new_vma->vm_private_data2 = NULL;
 			pol = mpol_dup(vma_policy(vma));
 			if (IS_ERR(pol))
 				goto out_free_vma;
diff --git a/mm/nommu.c b/mm/nommu.c
index 4ad47976b81c..e9143d859b00 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1614,6 +1614,8 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
 		region->vm_pgoff = new->vm_pgoff += npages;
 	}
 
+	new->vm_private_data2 = NULL;
+
 	if (new->vm_ops && new->vm_ops->open)
 		new->vm_ops->open(new);