Re: [PATCH v6 1/7] block: add a sanity check for non-write flush/fua bios

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 12/30/22 20:54, Niklas Cassel wrote:
> On Tue, Nov 08, 2022 at 02:55:38PM +0900, Damien Le Moal wrote:
>> From: Christoph Hellwig <hch@infradead.org>
>>
>> Check that the PREFUSH and FUA flags are only set on write bios,
>> given that the flush state machine expects that.
>>
>> Reported-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>> Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
>> Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
>> Reviewed-by: Hannes Reinecke <hare@suse.de>
>> ---
>>  block/blk-core.c | 13 ++++++++-----
>>  1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 17667159482e..d3446d38ba77 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -730,12 +730,15 @@ void submit_bio_noacct(struct bio *bio)
>> 	 * Filter flush bio's early so that bio based drivers without flush
>> 	 * support don't have to worry about them.
>> 	 */
>> -	if (op_is_flush(bio->bi_opf) &&
>> -	    !test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
>> -		bio->bi_opf &= ~(REQ_PREFLUSH | REQ_FUA);
>> -		if (!bio_sectors(bio)) {
>> -			status = BLK_STS_OK;
>> +	if (op_is_flush(bio->bi_opf)) {
>> +		if (WARN_ON_ONCE(bio_op(bio) != REQ_OP_WRITE))
>> 			goto end_io;
>> +		if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
> 
> Considering that blk_queue_write_cache() looks like this:
> 
> void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
> {
> 	if (wc)
> 		blk_queue_flag_set(QUEUE_FLAG_WC, q);
> 	else
> 		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
> 	if (fua)
> 		blk_queue_flag_set(QUEUE_FLAG_FUA, q);
> 	else
> 		blk_queue_flag_clear(QUEUE_FLAG_FUA, q);
> 
> 	wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
> }
> 
> It seems that you can have flag WC set, without having flag FUA set.
> 
> So should perhaps the line:
> 
>> +             if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
> 
> instead be:
> 
> if (!test_bit(QUEUE_FLAG_FUA, &q->queue_flags)) {

Need both. If there is no write cache or write cache is off, FUA is
implied and is useless.

> 
> 
> Kind regards,
> Niklas

-- 
Damien Le Moal
Western Digital Research