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btrfs: do not BUG_ON after failure to migrate space during truncation

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During truncation we reserve 2 metadata units when starting a transaction
(reserved space goes to fs_info->trans_block_rsv) and then attempt to
migrate 1 unit (min_size bytes) from fs_info->trans_block_rsv into the
local block reserve. If we ever fail we trigger a BUG_ON(), which should
never happen, because we reserved 2 units. However if we happen to fail
for some reason, we don't need to be so dire and hit a BUG_ON(), we can
just error out the truncation and, since this is highly unexpected,
surround the error check with WARN_ON(), to get an informative stack
trace and tag the branh as 'unlikely'. Also make the 'min_size' variable
const, since it's not supposed to ever change and any accidental change
could possibly make the space migration not so unlikely to fail.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Filipe Manana 2023-06-13 17:07:54 +01:00 • committed by David Sterba
parent df9f278239
commit 6822b3f708
1 changed files with 18 additions and 3 deletions
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21
fs/btrfs/inode.c
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@ -8344,7 +8344,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
int ret;
struct btrfs_trans_handle *trans;
u64 mask = fs_info->sectorsize - 1;
u64 min_size = btrfs_calc_metadata_size(fs_info, 1);
const u64 min_size = btrfs_calc_metadata_size(fs_info, 1);
if (!skip_writeback) {
ret = btrfs_wait_ordered_range(&inode->vfs_inode,
@ -8401,7 +8401,15 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
/* Migrate the slack space for the truncate to our reserve */
ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, rsv,
min_size, false);
BUG_ON(ret);
/*
* We have reserved 2 metadata units when we started the transaction and
* min_size matches 1 unit, so this should never fail, but if it does,
* it's not critical we just fail truncation.
*/
if (WARN_ON(ret)) {
btrfs_end_transaction(trans);
goto out;
}
trans->block_rsv = rsv;
@ -8449,7 +8457,14 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
btrfs_block_rsv_release(fs_info, rsv, -1, NULL);
ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
rsv, min_size, false);
BUG_ON(ret); /* shouldn't happen */
/*
* We have reserved 2 metadata units when we started the
* transaction and min_size matches 1 unit, so this should never
* fail, but if it does, it's not critical we just fail truncation.
*/
if (WARN_ON(ret))
break;
trans->block_rsv = rsv;
}