On Thu, 2020-09-17 at 19:45 +0100, Al Viro wrote: > On Thu, Sep 17, 2020 at 01:42:44PM -0400, Qian Cai wrote: > > > How much IO does it take to trigger that on your reproducer? > > > > That is something I don't know for sure because it is always reproducible by > > running the trinity fuzzer for a few seconds (32 threads). I did another run > > below (still with your patch applied) and then tried to capture some logs > > here: > > > > http://people.redhat.com/qcai/iov_iter_revert/ > > FWIW, there were several bugs in that patch: > * 'shortened' possibly left uninitialized > * possible error returns with reexpand not done > > Could you try this instead? This works fine. Thanks for taking care of this, Al. > > Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > --- > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 6611ef3269a8..43c165e796da 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -3091,11 +3091,10 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter > *iter) > ssize_t ret = 0; > struct file *file = iocb->ki_filp; > struct fuse_file *ff = file->private_data; > - bool async_dio = ff->fc->async_dio; > loff_t pos = 0; > struct inode *inode; > loff_t i_size; > - size_t count = iov_iter_count(iter); > + size_t count = iov_iter_count(iter), shortened = 0; > loff_t offset = iocb->ki_pos; > struct fuse_io_priv *io; > > @@ -3103,17 +3102,9 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter > *iter) > inode = file->f_mapping->host; > i_size = i_size_read(inode); > > - if ((iov_iter_rw(iter) == READ) && (offset > i_size)) > + if ((iov_iter_rw(iter) == READ) && (offset >= i_size)) > return 0; > > - /* optimization for short read */ > - if (async_dio && iov_iter_rw(iter) != WRITE && offset + count > i_size) > { > - if (offset >= i_size) > - return 0; > - iov_iter_truncate(iter, fuse_round_up(ff->fc, i_size - offset)); > - count = iov_iter_count(iter); > - } > - > io = kmalloc(sizeof(struct fuse_io_priv), GFP_KERNEL); > if (!io) > return -ENOMEM; > @@ -3129,15 +3120,22 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter > *iter) > * By default, we want to optimize all I/Os with async request > * submission to the client filesystem if supported. > */ > - io->async = async_dio; > + io->async = ff->fc->async_dio; > io->iocb = iocb; > io->blocking = is_sync_kiocb(iocb); > > + /* optimization for short read */ > + if (io->async && !io->write && offset + count > i_size) { > + iov_iter_truncate(iter, fuse_round_up(ff->fc, i_size - offset)); > + shortened = count - iov_iter_count(iter); > + count -= shortened; > + } > + > /* > * We cannot asynchronously extend the size of a file. > * In such case the aio will behave exactly like sync io. > */ > - if ((offset + count > i_size) && iov_iter_rw(iter) == WRITE) > + if ((offset + count > i_size) && io->write) > io->blocking = true; > > if (io->async && io->blocking) { > @@ -3155,6 +3153,7 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter > *iter) > } else { > ret = __fuse_direct_read(io, iter, &pos); > } > + iov_iter_reexpand(iter, iov_iter_count(iter) + shortened); > > if (io->async) { > bool blocking = io->blocking; >
