SLOB: fix bogus ksize calculation fix

This fixes the previous fix, which was completely wrong on closer
inspection. This version has been manually tested with a user-space
test harness and generates sane values. A nearly identical patch has
been boot-tested.

The problem arose from changing how kmalloc/kfree handled alignment
padding without updating ksize to match. This brings it in sync.

Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/mm/slob.c b/mm/slob.c
index 62b679dc660f..cb675d126791 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -514,9 +514,11 @@ size_t ksize(const void *block)
                 return 0;
 
         sp = (struct slob_page *)virt_to_page(block);
-        if (slob_page(sp))
-                return (((slob_t *)block - 1)->units - 1) * SLOB_UNIT;
-        else
+        if (slob_page(sp)) {
+                int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
+                unsigned int *m = (unsigned int *)(block - align);
+                return SLOB_UNITS(*m) * SLOB_UNIT;
+        } else
                 return sp->page.private;
 }