On 10/11/23 17:02, Jan Kara wrote:
xas_find_chunk() can be called only under RCU protection and thus tags
can be changing while it is working. Hence the code:
unsigned long data = *addr & (~0UL << offset);
if (data)
return __ffs(data);
is prone to 'data' being refetched from addr by the compiler and thus
calling __ffs() with 0 argument and undefined results.
Fix the problem by removing XA_CHUNK_SIZE == BITS_PER_LONG special case
completely. find_next_bit() gets this right and there's no performance
difference because it is inline and has the very same special branch for
const-sized bitmaps anyway.
Reported-by: Mirsad Todorovac <mirsad.todorovac@xxxxxxxxxxxx>
CC: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
include/linux/xarray.h | 9 ---------
1 file changed, 9 deletions(-)
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index cb571dfcf4b1..07700a2c8870 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1718,15 +1718,6 @@ static inline unsigned int xas_find_chunk(struct xa_state *xas, bool advance,
if (advance)
offset++;
- if (XA_CHUNK_SIZE == BITS_PER_LONG) {
- if (offset < XA_CHUNK_SIZE) {
- unsigned long data = *addr & (~0UL << offset);
- if (data)
- return __ffs(data);
- }
- return XA_CHUNK_SIZE;
- }
-
return find_next_bit(addr, XA_CHUNK_SIZE, offset);
}
Tested-by: Mirsad Todorovac <mirsad.todorovac@xxxxxxxxxxxx>
Best regards,
Mirsad
