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mm, dax: fix DAX deadlocks (COW fault)

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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] 0f90cc6609 mm, dax: fix DAX deadlocks
[2] 52a2b53ffd mm, dax: use i_mmap_unlock_write() in do_cow_fault()
[3] 843172978b dax: fix race between simultaneous faults
[4] 2e4cdab058 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>
This commit is contained in:
Yigal Korman 2015-11-16 14:09:15 +02:00 committed by Dan Williams
parent ee82c9ed41
commit 0df9d41ab5
1 changed files with 4 additions and 4 deletions
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8
mm/memory.c
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@ -3015,9 +3015,9 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma,
} else { } else {
/* /*
* The fault handler has no page to lock, so it holds * 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; goto uncharge_out;
} }
@ -3031,9 +3031,9 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma,
} else { } else {
/* /*
* The fault handler has no page to lock, so it holds * 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; return ret;
uncharge_out: uncharge_out: