On Thu, Mar 06, 2014 at 10:21:32AM -0800, Laura Abbott wrote: > We received several reports of bad page state when freeing CMA pages > previously allocated with alloc_contig_range: > > <1>[ 1258.084111] BUG: Bad page state in process Binder_A pfn:63202 > <1>[ 1258.089763] page:d21130b0 count:0 mapcount:1 mapping: (null) index:0x7dfbf > <1>[ 1258.096109] page flags: 0x40080068(uptodate|lru|active|swapbacked) > > Based on the page state, it looks like the page was still in use. The page > flags do not make sense for the use case though. Further debugging showed > that despite alloc_contig_range returning success, at least one page in the > range still remained in the buddy allocator. > > There is an issue with isolate_freepages_block. In strict mode (which CMA > uses), if any pages in the range cannot be isolated, > isolate_freepages_block should return failure 0. The current check keeps > track of the total number of isolated pages and compares against the size > of the range: > > if (strict && nr_strict_required > total_isolated) > total_isolated = 0; > > After taking the zone lock, if one of the pages in the range is not > in the buddy allocator, we continue through the loop and do not > increment total_isolated. If in the last iteration of the loop we isolate > more than one page (e.g. last page needed is a higher order page), the > check for total_isolated may pass and we fail to detect that a page was > skipped. The fix is to bail out if the loop immediately if we are in > strict mode. There's no benfit to continuing anyway since we need all > pages to be isolated. Additionally, drop the error checking based on > nr_strict_required and just check the pfn ranges. This matches with > what isolate_freepages_range does. > > Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx> Nice catch! stable stuff? Acked-by: Minchan Kim <minchan@xxxxxxxxxx> -- Kind regards, Minchan Kim -- 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>