The patch titled
Subject: dax: temporarily disable DAX PMD fault path
has been added to the -mm tree. Its filename is
dax-temporarily-disable-dax-pmd-fault-path.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/dax-temporarily-disable-dax-pmd-fault-path.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/dax-temporarily-disable-dax-pmd-fault-path.patch
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------------------------------------------------------
From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: dax: temporarily disable DAX PMD fault path
There is currently a deadlock in the DAX PMD fault path because it ends up
taking the same mapping->i_mmap_rwsem twice. The first take is a
i_mmap_lock_read() near the beginning of __dax_pmd_fault(), and the second
is __dax_pmd_fault() -> unmap_mapping_range() -> i_mmap_lock_write().
We are re-working the way that DAX does its locking for v4.4, so for now
just disable DAX PMD faults and fall back to PAGE_SIZE faults to make sure
we don't hit this deadlock.
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 7 +++++++
1 file changed, 7 insertions(+)
diff -puN fs/dax.c~dax-temporarily-disable-dax-pmd-fault-path fs/dax.c
--- a/fs/dax.c~dax-temporarily-disable-dax-pmd-fault-path
+++ a/fs/dax.c
@@ -534,6 +534,13 @@ int __dax_pmd_fault(struct vm_area_struc
unsigned long pfn;
int result = 0;
+ /*
+ * There is currently a deadlock in the DAX PMD fault path. Disable
+ * this path and fall back to the normal dax_fault() path for now
+ * while we rework locking.
+ */
+ return VM_FAULT_FALLBACK;
+
/* Fall back to PTEs if we're going to COW */
if (write && !(vma->vm_flags & VM_SHARED))
return VM_FAULT_FALLBACK;
_
Patches currently in -mm which might be from ross.zwisler@xxxxxxxxxxxxxxx are
revert-mm-take-i_mmap_lock-in-unmap_mapping_range-for-dax.patch
revert-dax-fix-race-between-simultaneous-faults.patch
dax-temporarily-disable-dax-pmd-fault-path.patch
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