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> -- Linux-cachefs mailing list Linux-cachefs@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/linux-cachefs