[PATCH] thp: Fix deadlock situation in vma_adjust with huge page in page cache

[PATCH] thp: Fix deadlock situation in vma_adjust with huge page in page cache

[Ning Qu]

In vma_adjust, the current code grabs i_mmap_mutex before calling
vma_adjust_trans_huge. This used to be fine until huge page in page
cache comes in. The problem is the underlying function
split_file_huge_page will also grab the i_mmap_mutex before splitting
the huge page in page cache. Obviously this is causing deadlock
situation.

This fix is to move the vma_adjust_trans_huge before grab the lock for
file, the same as what the function is currently doing for anonymous
memory.

Tested, everything works fine so far.

Signed-off-by: Ning Qu <quning@google.com>
---
mm/mmap.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 519ce78..accf1b3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -750,6 +750,8 @@ again:			remove_next = 1 + (end > next->vm_end);
		}
	}

+	vma_adjust_trans_huge(vma, start, end, adjust_next);
+
	if (file) {
		mapping = file->f_mapping;
		if (!(vma->vm_flags & VM_NONLINEAR)) {
@@ -773,8 +775,6 @@ again:			remove_next = 1 + (end > next->vm_end);
		}
	}

-	vma_adjust_trans_huge(vma, start, end, adjust_next);
-
	anon_vma = vma->anon_vma;
	if (!anon_vma && adjust_next)
		anon_vma = next->anon_vma;
-- 
1.8.3

RE: [PATCH] thp: Fix deadlock situation in vma_adjust with huge page in page cache

[Kirill A. Shutemov]

Ning Qu wrote:
> In vma_adjust, the current code grabs i_mmap_mutex before calling
> vma_adjust_trans_huge. This used to be fine until huge page in page
> cache comes in. The problem is the underlying function
> split_file_huge_page will also grab the i_mmap_mutex before splitting
> the huge page in page cache. Obviously this is causing deadlock
> situation.
> 
> This fix is to move the vma_adjust_trans_huge before grab the lock for
> file, the same as what the function is currently doing for anonymous
> memory.
> 
> Tested, everything works fine so far.
> 
> Signed-off-by: Ning Qu <quning@google.com>

Thanks, applied.

-- 
 Kirill A. Shutemov

[PATCH] thp: Fix deadlock situation in vma_adjust with huge page in page cache.

[Ning Qu]

In vma_adjust, the current code grabs i_mmap_mutex before calling
vma_adjust_trans_huge. This used to be fine until huge page in page
cache comes in. The problem is the underlying function
split_file_huge_page will also grab the i_mmap_mutex before splitting
the huge page in page cache. Obviously this is causing deadlock
situation.

This fix is to move the vma_adjust_trans_huge before grab the lock for
file, the same as what the function is currently doing for anonymous
memory. Tested, everything works fine so far.

Signed-off-by: Ning Qu <quning@google.com>
---
 mm/mmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 519ce78..accf1b3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -750,6 +750,8 @@ again: remove_next = 1 + (end > next->vm_end);
  }
  }

+ vma_adjust_trans_huge(vma, start, end, adjust_next);
+
  if (file) {
  mapping = file->f_mapping;
  if (!(vma->vm_flags & VM_NONLINEAR)) {
@@ -773,8 +775,6 @@ again: remove_next = 1 + (end > next->vm_end);
  }
  }

- vma_adjust_trans_huge(vma, start, end, adjust_next);
-
  anon_vma = vma->anon_vma;
  if (!anon_vma && adjust_next)
  anon_vma = next->anon_vma;
-- 
1.8.3