maple_tree: reset mas->index and mas->last on write retries

The following scenario can result in a race condition:

Consider a node with the following indices and values

	a<------->b<----------->c<--------->d
	    0xA        NULL          0xB

	CPU 1			  CPU 2
      ---------        		---------
	mas_set_range(a,b)
	mas_erase()
		-> range is expanded (a,c) because of null expansion

	mas_nomem()
	mas_unlock()
				mas_store_range(b,c,0xC)

The node now looks like:

	a<------->b<----------->c<--------->d
	    0xA        0xC          0xB

	mas_lock()
	mas_erase() <------ range of erase is still (a,c)

The node is now NULL from (a,c) but the write from CPU 2 should have been
retained and range (b,c) should still have 0xC as its value.  We can fix
this by re-intializing to the original index and last.  This does not need
a cc: Stable as there are no users of the maple tree which use internal
locking and this condition is only possible with internal locking.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sidhartha Kumar <[email protected]>
Reviewed-by: Liam R. Howlett <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions