On Mon, 2023-09-11 at 13:02 -0400, Jeff Layton wrote:
> On Thu, 2023-06-08 at 17:41 -0400, Dave Wysochanski wrote:
> > If a network filesystem using netfs implements a clamp_length()
> > function, it can set subrequest lengths smaller than a page size.
> > When we loop through the folios in netfs_rreq_unlock_folios() to
> > set any folios to be written back, we need to make sure we only
> > call folio_start_fscache() once for each folio. Otherwise,
> > this simple testcase:
> > mount -o fsc,rsize=1024,wsize=1024 127.0.0.1:/export /mnt/nfs
> > dd if=/dev/zero of=/mnt/nfs/file.bin bs=4096 count=1
> > 1+0 records in
> > 1+0 records out
> > 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.0126359 s, 324 kB/s
> > cat /mnt/nfs/file.bin > /dev/null
> >
> > will trigger an oops similar to the following:
> > ...
> > page dumped because: VM_BUG_ON_FOLIO(folio_test_private_2(folio))
> > ------------[ cut here ]------------
> > kernel BUG at include/linux/netfs.h:44!
> > ...
> > CPU: 5 PID: 134 Comm: kworker/u16:5 Kdump: loaded Not tainted 6.4.0-rc5
> > ...
> > RIP: 0010:netfs_rreq_unlock_folios+0x68e/0x730 [netfs]
> > ...
> > Call Trace:
> > <TASK>
> > netfs_rreq_assess+0x497/0x660 [netfs]
> > netfs_subreq_terminated+0x32b/0x610 [netfs]
> > nfs_netfs_read_completion+0x14e/0x1a0 [nfs]
> > nfs_read_completion+0x2f9/0x330 [nfs]
> > rpc_free_task+0x72/0xa0 [sunrpc]
> > rpc_async_release+0x46/0x70 [sunrpc]
> > process_one_work+0x3bd/0x710
> > worker_thread+0x89/0x610
> > kthread+0x181/0x1c0
> > ret_from_fork+0x29/0x50
> >
> > Signed-off-by: Dave Wysochanski <dwysocha@xxxxxxxxxx>
> > ---
> > fs/netfs/buffered_read.c | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
> > index 3404707ddbe7..0dafd970c1b6 100644
> > --- a/fs/netfs/buffered_read.c
> > +++ b/fs/netfs/buffered_read.c
> > @@ -21,6 +21,7 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
> > pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
> > size_t account = 0;
> > bool subreq_failed = false;
> > + bool folio_started;
>
> nit: I'd move this declaration inside the xas_for_each loop, and just
> initialize it to false there.
>
> >
> > XA_STATE(xas, &rreq->mapping->i_pages, start_epage);
> >
> > @@ -53,6 +54,7 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
> >
> > pg_end = folio_pos(folio) + folio_size(folio) - 1;
> >
> > + folio_started = false;
> > for (;;) {
> > loff_t sreq_end;
> >
> > @@ -60,8 +62,10 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
> > pg_failed = true;
> > break;
> > }
> > - if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))
> > + if (!folio_started && test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) {
> > folio_start_fscache(folio);
> > + folio_started = true;
> > + }
> > pg_failed |= subreq_failed;
> > sreq_end = subreq->start + subreq->len - 1;
> > if (pg_end < sreq_end)
>
>
> The logic looks correct though.
>
> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
David, can you review/merge this patch? This apparently fixes a panic
with NFS and fscache.
Thanks,
--
Jeff Layton <jlayton@xxxxxxxxxx>
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