In an attempt to make contiguous allocation routines more available to drivers, I have been experimenting with code similar to that used by alloc_gigantic_page(). While stressing this code with many other allocations and frees in progress, I would sometimes notice large 'leaks' of page ranges. I traced this down to the routine alloc_contig_range() itself. In commit 8ef5849fa8a2 the code was changed so that an -EBUSY returned by __alloc_contig_migrate_range() would not immediately return to the caller. Rather, processing continues so that test_pages_isolated() is eventually called. This is done because test_pages_isolated() has a tracepoint to identify the busy pages. However, it is possible (observed in my testing) that pages which were busy when __alloc_contig_migrate_range was called may become available by the time test_pages_isolated is called. Further, it is possible that the entire range can actually be allocated. Unfortunately, in this case the return code originally set by __alloc_contig_migrate_range (-EBUSY) is returned to the calller. Therefore, the caller assumes the range was not allocated and the pages are essentially leaked. The following patch simply updates the return code based on the value returned from test_pages_isolated. It is unlikely that we will hit this issue today based on the limited number of callers to alloc_contig_range. However, I have Cc'ed stable because if we do hit this issue it has the potential to leak a large number of pages. Mike Kravetz (1): mm/cma: fix alloc_contig_range ret code/potential leak mm/page_alloc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 2.13.6 -- 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>
