From: Mikulas Patocka <mpatocka@xxxxxxxxxx> Date: Thu, 14 Aug 2008 19:11:19 -0400 (EDT) [ Adding Alexander back to the CC: as he is seeing this same exact bug too, please keep him in the loop for testing. ] > So I tried the patch and found out that the corruption happens in > setup_command_line --- the first strcpy call corrupted the migratetype > map. > > Examining the problem further, it turned out that Johannes Weiner > committed new bootmem allocator to 2.6.27-rc1 and the allocator is broken. Ok, I was just looking at Alexander's debugging dump from my patch and in his case it pointed to kernel_physical_mapping_init() and I couldn't find any obvious problems there. But with the bug you found, it makes perfect sense, nice work! > 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". Excellent detective work! > 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. > > This patch fixes it (kernels 2.6.27-rc2 and 2.6.27-rc3 boot ok after the > patch). Johannes, please review the patch and submit it to Linus. > > 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> > > --- > mm/bootmem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: linux-2.6.27-rc2-orig/mm/bootmem.c > =================================================================== > --- linux-2.6.27-rc2-orig.orig/mm/bootmem.c 2008-08-15 00:10:38.000000000 +0200 > +++ linux-2.6.27-rc2-orig/mm/bootmem.c 2008-08-15 00:10:53.000000000 +0200 > @@ -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 > > -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
