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
echo 3 > /proc/sys/vm/drop_caches
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
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2210612
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Dave Wysochanski <[email protected]>
---
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..2cd3ccf4c439 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -47,12 +47,14 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
xas_for_each(&xas, folio, last_page) {
loff_t pg_end;
bool pg_failed = false;
+ bool folio_started;
if (xas_retry(&xas, folio))
continue;
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)
--
2.39.3