[PATCH] Btrfs: do not allow trimming when a fs is mounted with the nologreplay option

[fdmanana@kernel.org]

From: Filipe Manana <fdmanana@suse.com>

Whan a filesystem is mounted with the nologreplay mount option, which
requires it to be mounted in RO mode as well, we can not allow discard on
free space inside block groups, because log trees refer to extents that
are not pinned in a block group's free space cache (pinning the extents is
precisely the first phase of replaying a log tree).

So do not allow the fitrim ioctl to do anything when the filesystem is
mounted with the nologreplay option, because later it can be mounted RW
without that option, which causes log replay to happen and result in
either a failure to replay the log trees (leading to a mount failure), a
crash or some silent corruption.

Reported-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/ioctl.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 494f0f10d70e..01808934d21f 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -501,6 +501,16 @@ static noinline int btrfs_ioctl_fitrim(struct file *file, void __user *arg)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
+	/*
+	 * If the fs is mounted with nologreplay, which requires it to be
+	 * mounted in RO mode as well, we can not allow discard on free space
+	 * inside block groups, because log trees refer to extents that are not
+	 * pinned in a block group's free space cache (pinning the extents is
+	 * precisely the first phase of replaying a log tree).
+	 */
+	if (btrfs_test_opt(fs_info, NOLOGREPLAY))
+		return -EROFS;
+
 	rcu_read_lock();
 	list_for_each_entry_rcu(device, &fs_info->fs_devices->devices,
 				dev_list) {
-- 
2.11.0