From df1c357f25d808e30b216188330e708e09e1a412 Mon Sep 17 00:00:00 2001 From: Dave Wysochanski Date: Mon, 18 Sep 2023 14:17:11 +0100 Subject: [PATCH] netfs: Only call folio_start_fscache() one time for each folio 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: 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 Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers" Link: https://bugzilla.redhat.com/show_bug.cgi?id=2210612 Signed-off-by: Dave Wysochanski Reviewed-by: Jeff Layton Signed-off-by: David Howells Link: https://lore.kernel.org/r/20230608214137.856006-1-dwysocha@redhat.com/ # v1 Link: https://lore.kernel.org/r/20230915185704.1082982-1-dwysocha@redhat.com/ # v2 Signed-off-by: Linus Torvalds --- 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 3404707..2cd3ccf 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) -- 2.7.4