Commit 0df9d41a authored Nov 16, 2015 by Yigal Korman Committed by Dan Williams Nov 18, 2015

mm, dax: fix DAX deadlocks (COW fault)



DAX handling of COW faults has wrong locking sequence:
	dax_fault does i_mmap_lock_read
	do_cow_fault does i_mmap_unlock_write

Ross's commit[1] missed a fix[2] that Kirill added to Matthew's
commit[3].

Original COW locking logic was introduced by Matthew here[4].

This should be applied to v4.3 as well.

[1] 0f90cc66 mm, dax: fix DAX deadlocks
[2] 52a2b53f mm, dax: use i_mmap_unlock_write() in do_cow_fault()
[3] 84317297 dax: fix race between simultaneous faults
[4] 2e4cdab0 mm: allow page fault handlers to perform the COW

Cc: <stable@vger.kernel.org>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Jan Kara <jack@suse.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <matthew.r.wilcox@intel.com>
Acked-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Yigal Korman <yigal@plexistor.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

parent ee82c9ed

mm/memory.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -3015,9 +3015,9 @@ static int do_cow_fault(struct mm_struct mm, struct vm_area_struct vma,
		} else {
		/*
		* The fault handler has no page to lock, so it holds
		* i_mmap_lock for write to protect against truncate.
		* i_mmap_lock for read to protect against truncate.
		*/
		i_mmap_unlock_write(vma->vm_file->f_mapping);
		i_mmap_unlock_read(vma->vm_file->f_mapping);
		}
		goto uncharge_out;
		}
		@@ -3031,9 +3031,9 @@ static int do_cow_fault(struct mm_struct mm, struct vm_area_struct vma,
		} else {
		/*
		* The fault handler has no page to lock, so it holds
		* i_mmap_lock for write to protect against truncate.
		* i_mmap_lock for read to protect against truncate.
		*/
		i_mmap_unlock_write(vma->vm_file->f_mapping);
		i_mmap_unlock_read(vma->vm_file->f_mapping);
		}
		return ret;
		uncharge_out:

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