From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tao Ma Date: Mon, 12 Apr 2010 13:16:43 +0800 Subject: [Ocfs2-devel] [PATCH] ocfs2: avoid direct write if we fall back to buffered In-Reply-To: <4BC0B776020000460001DCCA@novprvlin0050.provo.novell.com> References: <4BC0B776020000460001DCCA@novprvlin0050.provo.novell.com> Message-ID: <4BC2ACBB.80909@oracle.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com Hi dong yang, Dong Yang Li wrote: > I still get a bug with this check and without my patch: yes, the check doesn't work actually in this case. > > > [16179.955148] (13400,1):ocfs2_truncate_file:465 ERROR: bug expression: le64_to_cpu(fe->i_size) != i_size_read(inode) > [16179.955157] (13400,1):ocfs2_truncate_file:465 ERROR: Inode 254789, inode i_size = 811008 != di i_size = 809011, i_flags = 0x1 > the call trace is the same. > > > the problem is this check in ocfs2_direct_IO_get_blocks just check if we are going beyond the blocks right now, > so if a direct write won't play with new blocks but extending the i_size still get a pass, like the error above said, di->i_size is 809011, using 198 blocks and the direct write end up with i_size 811008, just same 198 blocks. yeah, you are right. > > > IMHO, we can add this check back and fix this check, or we don't try to do direct write if we decided we can't in ocfs2_file_aio_write, after calling ocfs2_prepare_inode_for_write as my patch said. I think we only need to check this condition in get_blocks. So would you mind providing a patch? You old method is too aggressive actually. btw, I have created a small test script which will expose this bug easily. So you don't need to use the time-consuming fsstress test now. Just use it to test your fix. echo 'y'|mkfs.ocfs2 --fs-features=local,noinline-data -b 4K -C 4K $DEVICE 1000000 mount -t ocfs2 $DEVICE $MNT_DIR echo "foo" > $MNT_DIR/foo dd if=/dev/zero of=$MNT_DIR/foo bs=4K count=1 conv=notrunc oflag=direct echo "foo" > $MNT_DIR/foo # The kernel should panic here. Regards, Tao > > > Comments? ;-) > > > Br, > Li Dongyang >>>> Sunil Mushran 04/10/10 1:42 AM >>> > Li Dongyang wrote: >> On Friday 09 April 2010 11:32:10 Tao Ma wrote: >>> Hi Dongyang, >>> >>> Li Dongyang wrote: >>>> Hi, Tao, >>>> >>>> On Friday 09 April 2010 10:38:33 Tao Ma wrote: >>>>> Hi Dongyang, >>>>> >>>>> Li Dongyang wrote: >>>>>> This is because ocfs2_file_aio_write calls >>>>>> ocfs2_prepare_inode_for_write which sets direct_io to 0 if it finds out >>>>>> that direct IO would extend the file. But later we call >>>>>> __generic_file_aio_write which end's up calling >>>>>> generic_file_direct_write because the file has O_DIRECT flag.So every >>>>>> time we do a direct write extending the file, the inode->i_size gets >>>>>> inconsistent with the i_size on disk because we call >>>>>> generic_file_direct_write, and if we do a truncate after this, we will >>>>>> meet a bug in ocfs2_truncate_file. >>>>> yes we have O_DIRECT flag set and in __generic_file_aio_write it will >>>>> call generic_file_direct_write first and then trigger to >>>>> ocfs2_direct_IO. In this function we will check again and return 0. And >>>>> _generic_file_aio_write will fall back to buffered write if the directIO >>>>> can't write. Am I wrong somehow? >>>> yes ocfs2_direct_IO has some check, but it just check if we are >>>> appending(the i_size <= offset), if the offset < i_size and offset + >>>> count > i_size, it will do direct io anyway. seems we also can fix this >>>> by adding a check to ocfs2_direct_IO. >>> It is done by ocfs2_direct_IO_get_blocks. Just debug the kernel and you >>> will get what I mean. ;) >> Do you mean this section in ocfs2_direct_IO_get_blocks:? >> /* >> * Any write past EOF is not allowed because we'd be extending. >> */ >> if (create && (iblock + max_blocks) > inode_blocks) { >> ret = -EIO; >> goto bail; >> } >> >> I was using the linus tree >> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git >> and we don't have that check, but I can find this in the >> git://git.kernel.org/pub/scm/linux/kernel/git/jlbec/ocfs2.git, introduced by >> commit 564f8a3228879d6962edb3432d01bcd7499a67ec >> >> and now with this check I got what you mean, you are right, but I wonder why >> the linus tree doesn't have this check? and are we suppose to do with this? >> IMHO we can just push this commit to linus tree. > > commit 5fe878ae7f82fbf0830dbfaee4c5ca18f3aee442 > Author: Christoph Hellwig > Date: Tue Dec 15 16:47:50 2009 -0800 > > direct-io: cleanup blockdev_direct_IO locking > > This check was removed recently by the above patch. > >