From: Mikulas Patocka Date: Fri, 15 Aug 2008 07:40:17 +0000 (-0700) Subject: bootmem allocator: alloc_bootmem_core(): page-align the end offset X-Git-Tag: v2.6.27-rc4~100 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=627240aaa92a4dc00d25584910b5f205e963747b;p=linux-2.6-omap-h63xx.git 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 Acked-by: Johannes Weiner Cc: David Miller Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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