__GFP_NOFAIL specifies that the page allocator cannot fail to return memory. Allocators that call it may not even check for NULL upon returning.
It turns out GFP_NOWAIT | __GFP_NOFAIL or GFP_ATOMIC | __GFP_NOFAIL can actually return NULL. More interestingly, processes that are doing direct reclaim and have PF_MEMALLOC set may also return NULL for any __GFP_NOFAIL allocation. This patch fixes it so that the page allocator never actually returns NULL as expected for __GFP_NOFAIL. It turns out that no code actually does anything as crazy as GFP_ATOMIC | __GFP_NOFAIL currently, so this is more for correctness than a bug fix for that issue. Signed-off-by: David Rientjes <[email protected]> --- mm/page_alloc.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2535,17 +2535,19 @@ rebalance: } } - /* Atomic allocations - we can't balance anything */ - if (!wait) - goto nopage; - - /* Avoid recursion of direct reclaim */ - if (current->flags & PF_MEMALLOC) - goto nopage; - - /* Avoid allocations with no watermarks from looping endlessly */ - if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL)) - goto nopage; + if (likely(!(gfp_mask & __GFP_NOFAIL))) { + /* Atomic allocations - we can't balance anything */ + if (!wait) + goto nopage; + + /* Avoid recursion of direct reclaim */ + if (current->flags & PF_MEMALLOC) + goto nopage; + + /* Avoid allocations with no watermarks from looping forever */ + if (test_thread_flag(TIF_MEMDIE)) + goto nopage; + } /* * Try direct compaction. The first pass is asynchronous. Subsequent -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
