Re: [PATCH 2/2] btrfs: replace BUG_ON() in btrfs_csum_one_bio() with proper error handling

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2021/8/2 下午3:53, Nikolay Borisov wrote:
>
>
> On 2.08.21 г. 9:54, Qu Wenruo wrote:
>> The BUG_ON() in btrfs_csum_one_bio() means we're trying to submit a bio
>> while we don't have ordered extent for it at all.
>>
>> Normally this won't happen and is indeed a code logical error.
>>
>> But previous fix has already shown another possibility that, some call
>> sites don't handle error properly and submit the write bio after its
>> ordered extent has already been cleaned up.
>>
>> This patch will add an extra safe net by replacing the BUG_ON() to
>> proper error handling.
>>
>> And even if some day we hit a regression that we're submitting bio
>> without an ordered extent, we will return error and the pages will be
>> marked Error, and being caught properly.
>
> Would this hamper debugability? I.e it will result in some writes
> failing with an error, right?

Yes, it will make such corner case way more silent than before.

But IMHO the existing BUG_ON() is also overkilled.

Maybe converting it to WARN_ON() would be a good middle land?

Thanks,
Qu

>
>>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>   fs/btrfs/file-item.c | 14 +++++++++++++-
>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
>> index 2673c6ba7a4e..25205b9dad69 100644
>> --- a/fs/btrfs/file-item.c
>> +++ b/fs/btrfs/file-item.c
>> @@ -665,7 +665,19 @@ blk_status_t btrfs_csum_one_bio(struct btrfs_inode *inode, struct bio *bio,
>>
>>   		if (!ordered) {
>>   			ordered = btrfs_lookup_ordered_extent(inode, offset);
>> -			BUG_ON(!ordered); /* Logic error */
>> +			/*
>> +			 * No ordered extent mostly means the OE has been
>> +			 * removed (mostly for error handling). Normally for
>> +			 * such case we should not flush_write_bio(), but
>> +			 * end_write_bio().
>> +			 *
>> +			 * But an extra safe net will never hurt. Just error
>> +			 * out.
>> +			 */
>> +			if (unlikely(!ordered)) {
>> +				kvfree(sums);
>> +				return BLK_STS_IOERR;
>> +			}
>>   		}
>>
>>   		nr_sectors = BTRFS_BYTES_TO_BLKS(fs_info,
>>