The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5e753a817b2d5991dfe8a801b7b1e8e79a1c5a20 Mon Sep 17 00:00:00 2001

From: Anand Jain anand.jain@oracle.com Date: Fri, 30 Apr 2021 19:59:51 +0800 Subject: [PATCH] btrfs: fix unmountable seed device after fstrim

The following test case reproduces an issue of wrongly freeing in-use blocks on the readonly seed device when fstrim is called on the rw sprout device. As shown below.

Create a seed device and add a sprout device to it:

$ mkfs.btrfs -fq -dsingle -msingle /dev/loop0 $ btrfstune -S 1 /dev/loop0 $ mount /dev/loop0 /btrfs $ btrfs dev add -f /dev/loop1 /btrfs BTRFS info (device loop0): relocating block group 290455552 flags system BTRFS info (device loop0): relocating block group 1048576 flags system BTRFS info (device loop0): disk added /dev/loop1 $ umount /btrfs

Mount the sprout device and run fstrim:

$ mount /dev/loop1 /btrfs $ fstrim /btrfs $ umount /btrfs

Now try to mount the seed device, and it fails:

$ mount /dev/loop0 /btrfs mount: /btrfs: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.

Block 5292032 is missing on the readonly seed device:

$ dmesg -kt | tail <snip> BTRFS error (device loop0): bad tree block start, want 5292032 have 0 BTRFS warning (device loop0): couldn't read-tree root BTRFS error (device loop0): open_ctree failed

From the dump-tree of the seed device (taken before the fstrim). Block

5292032 belonged to the block group starting at 5242880:

$ btrfs inspect dump-tree -e /dev/loop0 | grep -A1 BLOCK_GROUP <snip> item 3 key (5242880 BLOCK_GROUP_ITEM 8388608) itemoff 16169 itemsize 24 block group used 114688 chunk_objectid 256 flags METADATA <snip>

From the dump-tree of the sprout device (taken before the fstrim).

fstrim used block-group 5242880 to find the related free space to free:

$ btrfs inspect dump-tree -e /dev/loop1 | grep -A1 BLOCK_GROUP <snip> item 1 key (5242880 BLOCK_GROUP_ITEM 8388608) itemoff 16226 itemsize 24 block group used 32768 chunk_objectid 256 flags METADATA <snip>

BPF kernel tracing the fstrim command finds the missing block 5292032 within the range of the discarded blocks as below:

kprobe:btrfs_discard_extent { printf("freeing start %llu end %llu num_bytes %llu:\n", arg1, arg1+arg2, arg2); }

freeing start 5259264 end 5406720 num_bytes 147456 <snip>

Fix this by avoiding the discard command to the readonly seed device.

Reported-by: Chris Murphy lists@colorremedies.com CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Anand Jain anand.jain@oracle.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 7a28314189b4..f1d15b68994a 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -1340,12 +1340,16 @@ int btrfs_discard_extent(struct btrfs_fs_info *fs_info, u64 bytenr, stripe = bbio->stripes; for (i = 0; i < bbio->num_stripes; i++, stripe++) { u64 bytes; + struct btrfs_device *device = stripe->dev;

- if (!stripe->dev->bdev) { + if (!device->bdev) { ASSERT(btrfs_test_opt(fs_info, DEGRADED)); continue; }

+ if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) + continue; + ret = do_discard_extent(stripe, &bytes); if (!ret) { discarded_bytes += bytes;