The patch titled
bootmem allocator: alloc_bootmem_core(): page-align the end offset
has been added to the -mm tree. Its filename is
bootmem-allocator-alloc_bootmem_core-page-align-the-end-offset.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: bootmem allocator: alloc_bootmem_core(): page-align the end offset
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
This is the minimal sequence that jams the allocator:
void *p, *q, *r;
p = alloc_bootmem(PAGE_SIZE);
q = alloc_bootmem(64);
free_bootmem(p, PAGE_SIZE);
p = alloc_bootmem(PAGE_SIZE);
r = alloc_bootmem(64);
after this sequence (assuming that the allocator was empty or page-aligned
before), pointer "q" will be equal to pointer "r".
What's hapenning inside the allocator:
p = alloc_bootmem(PAGE_SIZE);
in allocator: last_end_off == PAGE_SIZE, bitmap contains bits 10000...
q = alloc_bootmem(64);
in allocator: last_end_off == PAGE_SIZE + 64, bitmap contains 11000...
free_bootmem(p, PAGE_SIZE);
in allocator: last_end_off == PAGE_SIZE + 64, bitmap contains 01000...
p = alloc_bootmem(PAGE_SIZE);
in allocator: last_end_off == PAGE_SIZE, bitmap contains 11000...
r = alloc_bootmem(64);
and now:
it finds bit "2", as a place where to allocate (sidx)
it hits the condition
if (bdata->last_end_off && PFN_DOWN(bdata->last_end_off) + 1 == sidx))
start_off = ALIGN(bdata->last_end_off, align);
-you can see that the condition is true, so it assigns start_off =
ALIGN(bdata->last_end_off, align); (that is PAGE_SIZE) and allocates
over already allocated block.
With the patch it tries to continue at the end of previous allocation only
if the previous allocation ended in the middle of the page.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/bootmem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/bootmem.c~bootmem-allocator-alloc_bootmem_core-page-align-the-end-offset mm/bootmem.c
--- a/mm/bootmem.c~bootmem-allocator-alloc_bootmem_core-page-align-the-end-offset
+++ a/mm/bootmem.c
@@ -473,7 +473,7 @@ find_block:
goto find_block;
}
- if (bdata->last_end_off &&
+ if (bdata->last_end_off & (PAGE_SIZE - 1) &&
PFN_DOWN(bdata->last_end_off) + 1 == sidx)
start_off = ALIGN(bdata->last_end_off, align);
else
_
Patches currently in -mm which might be from mpatocka@xxxxxxxxxx are
bootmem-allocator-alloc_bootmem_core-page-align-the-end-offset.patch
linux-next.patch
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