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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: <[email protected]>
Cc: Boaz Harrosh <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Acked-by: Ross Zwisler <[email protected]>
Signed-off-by: Yigal Korman <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
This commit is contained in:
Yigal Korman 2015-11-16 14:09:15 +02:00 • committed by Dan Williams
commit 0df9d41ab5
1 changed files with 4 additions and 4 deletions
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8
mm/memory.c
View file

@ -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: