Hi, On Wed, 2013-08-21 at 13:58 -0700, Andrew Morton wrote: > On Wed, 21 Aug 2013 17:42:12 +0100 Steven Whitehouse <swhiteho@xxxxxxxxxx> wrote: > > > > I don't think the change is harmful. The worst case scenario is race with > > > write or truncate, but it's valid to return EOF in this case. > > > > > > What scenario do you have in mind? > > > > > > > 1. File open on node A > > 2. Someone updates it on node B by extending the file > > 3. Someone reads the file on node A beyond end of original file size, > > but within end of new file size as updated by node B. Without the patch > > this works, with it, it will fail. The reason being the i_size would not > > be up to date until after readpage(s) has been called. > > > > I think this is likely to be an issue for any distributed fs using > > do_generic_file_read(), although it would certainly affect GFS2, since > > the locking is done at page cache level, > > Boy, that's rather subtle. I'm surprised that the generic filemap.c > stuff works at all in that sort of scenario. > > Can we put the i_size check down in the no_cached_page block? afaict > that will solve the problem without breaking GFS2 and is more > efficient? > Well I think is even more subtle, since it relies on ->readpages updating the file size, even if it has failed to actually read the required pages :-) Having said that, we do rely on ->readpages updating the inode size elsewhere in this function, as per the block comment immediately following the page_ok label. This should work for GFS2 though, and I did check OCFS2 and I think it should work for them too, Steve. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>