From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: Oops in __free_pages_ok (pre7-1) (Long) From: "Juan J. Quintela" Date: 02 May 2000 03:08:02 +0200 In-Reply-To: "Juan J. Quintela"'s message of "02 May 2000 01:29:26 +0200" Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: linux-mm@kvack.org, Linus Torvalds , Andrea Arcangeli , Kanoj Sarcar List-ID: Hi several people have reported Oops in __free_pages_ok, after a BUG() in page_alloc.h. This happens in 2.3.99-pre[67]. The BUGs are: if (page->mapping) BUG(); and if (PageSwapCache(page)) BUG(); somebody reported to me that he obtained the BUG: if (PageLocked(page)) BUG(); I have found that this patch solves the Oops for me. (I know that this is not the proper solution, could people test this patch and mail me if the Oops disappear/or go worst? I am trying to isolate the problem. Now I get one kill of the process from the VM, I am interested to know if this is the case for the rest of the people with this problem. I have read the comments from Andrea in this list about that PG_swap_entry bit should be only a optimization, never produce instability. I have checked that with the following patch (i.e. the only place when we set that bit) I don't get more Oops. This bit is only used in three places in the kernel: mm/memory.c:1056:do_swap_page()::SetPageSwapEntry(page); The only place where it is set mm/swapfile.c:210:acquire_swap_entry(): if (!PageSwapEntry(page)) Here we check if it is set, and if true, we check that the values are valid. mm/swap_state.c:134: ClearPageSwapEntry(page); We clear the bit in free_page_and_swap_cache(), but I am not sure that it is the only place when it must be deleted. Comments really appreciated. It appears that we forgot to remove some bits/values when we free a page. It has been several patches in this list regarding the swap_entry bit, but not agreement in which is the correct one. I hope this help to somebody understand where is the problem, or at least give me some hint where can be the problem. Thanks in advance, Juan. diff -u -urN --exclude=CVS --exclude=*~ --exclude=.#* pre7-1plus/mm/memory.c lin ux/mm/memory.c --- pre7-1plus/mm/memory.c Tue Apr 25 00:46:18 2000 +++ linux/mm/memory.c Tue May 2 00:36:13 2000 @@ -1053,7 +1053,7 @@ pte = mk_pte(page, vma->vm_page_prot); - SetPageSwapEntry(page); + /* SetPageSwapEntry(page); */ /* * Freeze the "shared"ness of the page, ie page_count + swap_count. -- In theory, practice and theory are the same, but in practice they are different -- Larry McVoy -- 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.eu.org/Linux-MM/