From fe910d20e2d8e0736bbea9c1efe6a49535e807ea Mon Sep 17 00:00:00 2001 From: Anand Jain Date: Fri, 30 Apr 2021 19:59:51 +0800 Subject: [PATCH] btrfs: fix unmountable seed device after fstrim commit 5e753a817b2d5991dfe8a801b7b1e8e79a1c5a20 upstream. 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 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 item 3 key (5242880 BLOCK_GROUP_ITEM 8388608) itemoff 16169 itemsize 24 block group used 114688 chunk_objectid 256 flags METADATA >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 item 1 key (5242880 BLOCK_GROUP_ITEM 8388608) itemoff 16226 itemsize 24 block group used 32768 chunk_objectid 256 flags METADATA 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 Fix this by avoiding the discard command to the readonly seed device. Reported-by: Chris Murphy CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Filipe Manana Signed-off-by: Anand Jain Signed-off-by: David Sterba Signed-off-by: Sudip Mukherjee Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/extent-tree.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 728d75e8e792..73ebe0c5fdbc 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -1297,16 +1297,20 @@ int btrfs_discard_extent(struct btrfs_fs_info *fs_info, u64 bytenr, for (i = 0; i < bbio->num_stripes; i++, stripe++) { u64 bytes; struct request_queue *req_q; + struct btrfs_device *device = stripe->dev; - if (!stripe->dev->bdev) { + if (!device->bdev) { ASSERT(btrfs_test_opt(fs_info, DEGRADED)); continue; } - req_q = bdev_get_queue(stripe->dev->bdev); + req_q = bdev_get_queue(device->bdev); if (!blk_queue_discard(req_q)) continue; - ret = btrfs_issue_discard(stripe->dev->bdev, + if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) + continue; + + ret = btrfs_issue_discard(device->bdev, stripe->physical, stripe->length, &bytes); -- 2.34.1