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authorMikulas Patocka <mpatocka@redhat.com>2008-08-15 00:40:17 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-08-15 08:35:41 -0700
commit627240aaa92a4dc00d25584910b5f205e963747b (patch)
tree7e05e87ecc48b57de8c2eeb872ce7a0102c2af3b
parentb635acec48bcaa9183fcbf4e3955616b0d4119b5 (diff)
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>
-rw-r--r--mm/bootmem.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/bootmem.c b/mm/bootmem.c
index 4af15d0340a..e023c68b025 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