On Friday 22 February 2013 02:01 AM, Yinghai Lu wrote: > On Thu, Feb 21, 2013 at 12:10 PM, Vineet Gupta > <Vineet.Gupta1@xxxxxxxxxxxx> wrote: >> This came to light when calling memblock allocator from arc port (for >> copying flattended DT). If a "0" alignment is passed, the allocator >> round_up() call incorrectly rounds up the size to 0. >> >> round_up(num, alignto) => ((num - 1) | (alignto -1)) + 1 >> >> While the obvious allocation failure causes kernel to panic, it is >> better to warn the caller to fix the code. >> >> Tejun suggested that instead of BUG_ON(!align) - which might be >> ineffective due to pending console init and such, it is better to >> WARN_ON, and continue the boot with a reasonable default align. >> >> Caller passing @size need not be handled similarly as the subsequent >> panic will indicate that anyhow. >> >> Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx> >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >> Cc: Tejun Heo <tj@xxxxxxxxxx> >> Cc: Yinghai Lu <yinghai@xxxxxxxxxx> >> Cc: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx> >> Cc: Ingo Molnar <mingo@xxxxxxxxxx> >> Cc: linux-mm@xxxxxxxxx >> Cc: linux-kernel@xxxxxxxxxxxxxxx >> --- >> mm/memblock.c | 3 +++ >> 1 files changed, 3 insertions(+), 0 deletions(-) >> >> diff --git a/mm/memblock.c b/mm/memblock.c >> index 1bcd9b9..f3804bd 100644 >> --- a/mm/memblock.c >> +++ b/mm/memblock.c >> @@ -824,6 +824,9 @@ static phys_addr_t __init memblock_alloc_base_nid(phys_addr_t size, >> /* align @size to avoid excessive fragmentation on reserved array */ >> size = round_up(size, align); >> >> + if (WARN_ON(!align)) >> + align = __alignof__(long long); >> + > the checking should be put before round_up? Oops my bad. Interestingly however, I did test this exact patch on ARC before sending out - passing @align = 0 to make it hit the WARN. It prints the warning, and uses @size=0, @align=8 for memblock_find_in_range_node() and successfully allocates memory as opposed to failure for @size=0, @align=0 scenario. This is kind of weird. Anyhow I'll send the updated patch to fix the gotcha ! Thx, -Vineet -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>