On Fri, 2024-04-26 at 12:15 +0100, David Howells wrote:
> In netfs_perform_write(), when the file is marked NETFS_ICTX_WRITETHROUGH
> or O_*SYNC or RWF_*SYNC was specified, write-through caching is performed
> on a buffered file. When setting up for write-through, we flush any
> conflicting writes in the region and wait for the write to complete,
> failing if there's a write error to return.
>
> The issue arises if we're writing at or above the EOF position because we
> skip the flush and - more importantly - the wait. This becomes a problem
> if there's a partial folio at the end of the file that is being written out
> and we want to make a write to it too. Both the already-running write and
> the write we start both want to clear the writeback mark, but whoever is
> second causes a warning looking something like:
>
> ------------[ cut here ]------------
> R=00000012: folio 11 is not under writeback
> WARNING: CPU: 34 PID: 654 at fs/netfs/write_collect.c:105
> ...
> CPU: 34 PID: 654 Comm: kworker/u386:27 Tainted: G S ...
> ...
> Workqueue: events_unbound netfs_write_collection_worker
> ...
> RIP: 0010:netfs_writeback_lookup_folio
>
> Fix this by making the flush-and-wait unconditional. It will do nothing if
> there are no folios in the pagecache and will return quickly if there are
> no folios in the region specified.
>
> Further, move the WBC attachment above the flush call as the flush is going
> to attach a WBC and detach it again if it is not present - and since we
> need one anyway we might as well share it.
>
> Fixes: 41d8e7673a77 ("netfs: Implement a write-through caching option")
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-lkp/202404161031.468b84f-oliver.sang@xxxxxxxxx
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Eric Van Hensbergen <ericvh@xxxxxxxxxx>
> cc: Latchesar Ionkov <lucho@xxxxxxxxxx>
> cc: Dominique Martinet <asmadeus@xxxxxxxxxxxxx>
> cc: Christian Schoenebeck <linux_oss@xxxxxxxxxxxxx>
> cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
> cc: netfs@xxxxxxxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> cc: linux-mm@xxxxxxxxx
> cc: v9fs@xxxxxxxxxxxxxxx
> cc: linux-afs@xxxxxxxxxxxxxxxxxxx
> cc: linux-cifs@xxxxxxxxxxxxxxx
> ---
> fs/netfs/buffered_write.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
> index 9a0d32e4b422..07aff231926c 100644
> --- a/fs/netfs/buffered_write.c
> +++ b/fs/netfs/buffered_write.c
> @@ -172,15 +172,14 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
> if (unlikely(test_bit(NETFS_ICTX_WRITETHROUGH, &ctx->flags) ||
> iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC))
> ) {
> - if (pos < i_size_read(inode)) {
> - ret = filemap_write_and_wait_range(mapping, pos, pos + iter->count);
> - if (ret < 0) {
> - goto out;
> - }
> - }
> -
> wbc_attach_fdatawrite_inode(&wbc, mapping->host);
>
> + ret = filemap_write_and_wait_range(mapping, pos, pos + iter->count);
> + if (ret < 0) {
> + wbc_detach_inode(&wbc);
> + goto out;
> + }
> +
> wreq = netfs_begin_writethrough(iocb, iter->count);
> if (IS_ERR(wreq)) {
> wbc_detach_inode(&wbc);
>
Reviewed-by: Jeffrey Layton <jlayton@xxxxxxxxxx>
