From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 8C51D6B005D for ; Sun, 2 Aug 2009 06:43:27 -0400 (EDT) Date: Sun, 2 Aug 2009 11:54:13 +0100 (BST) From: Hugh Dickins Subject: Re: mm/hugetlb: GFP_KERNEL allocation under spinlock? In-Reply-To: <4A755201.1010200@gmail.com> Message-ID: References: <4A755201.1010200@gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Jiri Slaby Cc: linux-mm@kvack.org, Mel Gorman List-ID: On Sun, 2 Aug 2009, Jiri Slaby wrote: > > could anybody please confirm this cannot happen? I'm no authority on hugetlb.c nowadays: you'll have studied this in more detail than I have, so please don't believe me. (And I'm no longer at my old address, but lkml's enjoying a quiet Sunday.) > > hugetlb_fault() > -> spin_lock() > -> hugetlb_cow() > -> alloc_huge_page() > -> vma_needs_reservation() > -> region_chg() (either of the 2) > -> kmalloc(*, GFP_KERNEL) > > Thanks. That should be taken care of by the successful vma_needs_reservation() on the same address in hugetlb_fault(), before taking page_table_lock, shouldn't it? It is possible that a hugetlb_vmtruncate() comes in between that vma_needs_reservation() and taking the page_table_lock, which could remove the region (or "nrg") needed. But if that's the case then the pte_same test immediately after taking page_table_lock should catch it: we're in the part of hugetlb_fault() dealing with !huge_pte_none, whereas truncation would have made it huge_pte_none (and it won't get to freeing the reservations before it's nullified the page tables, holding page_table_lock). Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org