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Subject[PATCH] bitmap: fix a unproper remap when mpol_rebind_nodemask()
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Consider one situation:

The app have two vmas which mbind() to node 1 and node3 respectively,
and its cpuset.mems is 0-3, now set its cpuset.mems to 1,3, according
to current bitmap_remap(), we got:

1 => 3
3 => 3

This maybe confused because node 1,3 have already in the new settiing
region but both nodes are binded to the same node 3 now.

Actually we found the situation on a very old libvirt and qemu, but
this can be easily reproduced in the current kernel, so we try to fix
it.

A possible fix way is to ignore the bits in @src have already existed
in @new.

Signed-off-by: Yi Wang <wang.yi59@zte.com.cn>
---
lib/bitmap.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index b18e31ea6e66..b77bf1b3852e 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -1006,8 +1006,8 @@ unsigned int bitmap_ord_to_pos(const unsigned long *buf, unsigned int ord, unsig
* @dst point to the same location, then this routine copies @src
* to @dst.
*
- * The positions of unset bits in @old are mapped to themselves
- * (the identify map).
+ * The positions of unset bits in @old or bits in @src have already
+ * existed in @new are mapped to themselves (the identify map).
*
* Apply the above specified mapping to @src, placing the result in
* @dst, clearing any bits previously set in @dst.
@@ -1033,7 +1033,7 @@ void bitmap_remap(unsigned long *dst, const unsigned long *src,
for_each_set_bit(oldbit, src, nbits) {
int n = bitmap_pos_to_ord(old, oldbit, nbits);

- if (n < 0 || w == 0)
+ if (n < 0 || w == 0 || test_bit(oldbit, new))
set_bit(oldbit, dst); /* identity map */
else
set_bit(bitmap_ord_to_pos(new, n % w, nbits), dst);
--
2.33.0.rc0.dirty
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