Re: btrfs_direct_IO oops

From: Al Viro
Date: Mon Oct 10 2016 - 11:55:12 EST


On Mon, Oct 10, 2016 at 09:11:22AM -0400, Dave Jones wrote:

> My compiler choked on that, but I fixed it up. The printk didn't
> trigger though..
>
> idx = 0, offset = 0
> curbuf = 0, nrbufs = 1, buffers = 16
> [ffffffffb9a21100 ffffea00126019c0 0 4096]
> [ (null) ffffea0013746440 0 0]
> [ (null) ffffea00132956c0 0 0]
> [ (null) ffffea0013295700 0 0]
> [ (null) ffffea0013295740 0 0]
> [ (null) ffffea0013295780 0 0]
> [ (null) ffffea00132957c0 0 0]
> [ (null) ffffea0013595c00 0 0]
> [ (null) ffffea0012b1b6c0 0 0]
> [ (null) (null) 0 0]
> [ (null) (null) 0 0]
> [ (null) (null) 0 0]
> [ (null) (null) 0 0]
> [ (null) (null) 0 0]
> [ (null) (null) 0 0]
> [ (null) (null) 0 0]
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 13581 at lib/iov_iter.c:327 sanity+0x102/0x150
> CPU: 1 PID: 13581 Comm: trinity-c17 Not tainted 4.8.0-think+ #9
> ffffc90000963ae8
> ffffffffb93e22d1
> 0000000000000000
> 0000000000000000
>
> ffffffffb9c1e1cb
> ffffffffb93fa5b2
> ffffc90000963b28
> ffffffffb908b010
>
> 00000147d43c0e7f
> ffffffffb9c1e1cb
> 0000000000000147
> 0000000000000010

What are these from? Confused...

> Call Trace:

[via splice_direct_to_actor()]

Hmmm... I think I see it. Could you try the following (on top of debugging
in lib/iov_iter.c) and see if anything triggers?

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index bfc2aa7..b63d8c5 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -319,7 +319,7 @@ xfs_file_dio_aio_read(
data = *to;
ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
xfs_get_blocks_direct, NULL, NULL, 0);
- if (ret > 0) {
+ if (ret >= 0) {
iocb->ki_pos += ret;
iov_iter_advance(to, ret);
}
diff --git a/mm/filemap.c b/mm/filemap.c
index 68f1813..88e5ddd 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1935,7 +1935,7 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
file_accessed(file);

retval = mapping->a_ops->direct_IO(iocb, &data);
- if (retval > 0) {
+ if (retval >= 0) {
iocb->ki_pos += retval;
iov_iter_advance(iter, retval);
}