2014-03-21 3:10 GMT+04:00 Jeff Layton <jlayton@xxxxxxxxxx>: > On Fri, 21 Mar 2014 05:56:04 +0900 > Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > >> Jeff Layton wrote: >> > That's expected behavior. The kernel believes that the file is frozen in >> > length so it returns short read() calls until the size is updated. >> >> The "size is updated" means "stat() detects the growth of file size", >> doesn't it? Then, the former is expected behavior. >> >> > >> > cache=loose is very much not recommended for use when you have multiple >> > hosts accessing files on the server (or access by processes on the >> > server itself). It only gives you "loose" cache coherency. The whole >> > point of it is to allow the client to cache data even when the protocol >> > says that it shouldn't. >> >> But why is the latter ( "read() returns non-0 when stat() detects the growth >> of file size but the data actually read is '\0'" ) is expected behavior? >> It sounds like a bug that the client caches '\0' (data nobody has ever wrote) >> instead of '.' (data somebody wrote when the file size grew). >> > > Yeah, that sounds wrong. What should happen is that the cache is > invalidated when the size changes. It's possible there is a race in > that code however. The locking around it is pretty sloppy... When fstat() get a new file size it sets CIFS_I(inode)->invalid_mapping to true but do not revalidate the cache. Then generic_file_aio_read() reads the wrong data. I think we need to check if CIFS_I(inode)->invalid_mapping is true and revalidate the cache before calling generic_file_aio_read() in file->f_ops->aio_read(). Now cache revalidation happens in lookup/open and mmap codepaths only for cache=loose. Of course, cache=loose is not recommended for this sort of work flow and cache=strict should be used to provide a data coherency between several machines. -- Best regards, Pavel Shilovsky. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
