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authorMikulas Patocka <mpatocka@redhat.com>2008-08-15 11:40:17 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-08-15 19:35:41 +0400
commit627240aaa92a4dc00d25584910b5f205e963747b (patch)
tree7e05e87ecc48b57de8c2eeb872ce7a0102c2af3b /mm
parentb635acec48bcaa9183fcbf4e3955616b0d4119b5 (diff)
downloadlinux-627240aaa92a4dc00d25584910b5f205e963747b.tar.xz
bootmem allocator: alloc_bootmem_core(): page-align the end offset
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@redhat.com> Acked-by: Johannes Weiner <hannes@saeurebad.de> Cc: David Miller <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/bootmem.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/bootmem.c b/mm/bootmem.c
index 4af15d0340ad..e023c68b0255 100644
--- a/mm/bootmem.c
+++ b/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