On Thu, 2024-03-07 at 22:41 +1100, NeilBrown wrote:
> On Thu, 07 Mar 2024, Jeff Layton wrote:
> > On Wed, 2024-02-28 at 10:23 +1100, NeilBrown wrote:
> > > when AOP_WRITEPAGE_ACTIVATE is returned (as NFS does when it detects
> > > congestion) it is important that the folio is redirtied.
> > > nfs_writepage_locked() doesn't do this, so files can become corrupted as
> > > writes can be lost.
> > >
> > > Note that this is not needed in v6.8 as AOP_WRITEPAGE_ACTIVATE cannot be
> > > returned. It is needed for kernels v5.18..v6.7. Prior to 6.3 the patch
> > > is different as it needs to mention "page", not "folio".
> > >
> >
> > Neil, I have a question about the above statement. In Linus's tree as of
> > this morning (v6.8-rc7-ish), it does this in nfs_writepages_locked:
> >
> > if (wbc->sync_mode == WB_SYNC_NONE &&
> > NFS_SERVER(inode)->write_congested)
> > return AOP_WRITEPAGE_ACTIVATE;
> >
> > The only caller of nfs_writepages_locked, and I don't see where it
> > redirties the page. Why don't we need this in v6.8?
>
> You are right - it doesn't redirty anything. But there is no bug
> here....
> I didn't see it at first either, but the only caller of
> nfs_writepage_locked() is nfs_wb_folio() (as you say) and that always
> passes a wbc with .sync_mode = WB_SYNC_ALL. So sync_mode is never
> WB_SYNC_NODE and the code snippet you included above is dead code. I've
> already posted a patch to Trond and Anna to remove that code.
>
> Thanks for the review!
>
Thanks Neil,
I missed that bit about the sync_mode. I sent a R-b for your other patch
too.
Cheers,
Jeff
> >
> >
> > > Reported-and-tested-by: Jacek Tomaka <Jacek.Tomaka@xxxxxxxxx>
> > > Fixes: 6df25e58532b ("nfs: remove reliance on bdi congestion")
> > > Signed-off-by: NeilBrown <neilb@xxxxxxx>
> > > ---
> > > fs/nfs/write.c | 4 +++-
> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/nfs/write.c b/fs/nfs/write.c
> > > index b664caea8b4e..9e345d3c305a 100644
> > > --- a/fs/nfs/write.c
> > > +++ b/fs/nfs/write.c
> > > @@ -668,8 +668,10 @@ static int nfs_writepage_locked(struct folio *folio,
> > > int err;
> > >
> > > if (wbc->sync_mode == WB_SYNC_NONE &&
> > > - NFS_SERVER(inode)->write_congested)
> > > + NFS_SERVER(inode)->write_congested) {
> > > + folio_redirty_for_writepage(wbc, folio);
> > > return AOP_WRITEPAGE_ACTIVATE;
> > > + }
> > >
> > > nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGE);
> > > nfs_pageio_init_write(&pgio, inode, 0, false,
> >
> > --
> > Jeff Layton <jlayton@xxxxxxxxxx>
> >
>
--
Jeff Layton <jlayton@xxxxxxxxxx>
