From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [RFC][PATCH] EXT3: problem with page fault inside a transaction References: <87mz82vzy1.fsf@sw.ru> <20061011234330.efae4265.akpm@osdl.org> From: Dmitriy Monakhov Date: Thu, 12 Oct 2006 11:53:56 +0400 In-Reply-To: <20061011234330.efae4265.akpm@osdl.org> (Andrew Morton's message of "Wed, 11 Oct 2006 23:43:30 -0700") Message-ID: <87lknmgeaz.fsf@sw.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Dmitriy Monakhov , Linux Kernel , Linux Memory Management , devel@openvz.org, ext2-devel@lists.sourceforge.net, Andrey Savochkin List-ID: Andrew Morton writes: > On Thu, 12 Oct 2006 09:57:26 +0400 > Dmitriy Monakhov wrote: > >> While reading Andrew's generic_file_buffered_write patches i've remembered >> one more EXT3 issue.journal_start() in prepare_write() causes different ranking >> violations if copy_from_user() triggers a page fault. It could cause >> GFP_FS allocation, re-entering into ext3 code possibly with a different >> superblock and journal, ranking violation of journalling serialization >> and mmap_sem and page lock and all other kinds of funny consequences. > > With the stuff Nick and I are looking at, we won't take pagefaults inside > prepare_write()/commit_write() any more. I'sorry may be i've missed something, but how cant you prevent this? Let's look at generic_file_buffered_write: #### force page fault fault_in_pages_readable(); ### find and lock page __grab_cache_page() #### allocate blocks.This may result in low memory condition #### try_to_free_pages->shrink_caches() and etc. a_ops->prepare_write() ### can anyone guarantee that page fault hasn't happened by now ? ### user space buffer swapped out, or became invalid. filemap_copy_from_user() > >> Our customers complain about this issue. > > Really? How often? I have't concrete statistic > > What on earth are they doing to trigger this? writev() without the 2.6.18 > writev() bugfix? -- 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