On 2022/2/23 2:27, Mike Snitzer wrote:
> On Wed, Feb 09 2022 at 4:37P -0500,
> Zhang Yi <yi.zhang@xxxxxxxxxx> wrote:
>
>> We found a NULL pointer dereference problem when using dm-mpath target.
>> The problem is if we submit IO between loading and binding the table,
>> we could neither get a valid dm_target nor a valid dm table when
>> submitting request in dm_mq_queue_rq(). BIO based dm target could
>> handle this case in dm_submit_bio(). This patch fix this by checking
>> the mapping table before submitting request.
>>
>> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
>> ---
>> drivers/md/dm-rq.c | 11 +++++++++--
>> 1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
>> index 579ab6183d4d..af2cf71519e9 100644
>> --- a/drivers/md/dm-rq.c
>> +++ b/drivers/md/dm-rq.c
>> @@ -499,8 +499,15 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
>>
>> if (unlikely(!ti)) {
>> int srcu_idx;
>> - struct dm_table *map = dm_get_live_table(md, &srcu_idx);
>> -
>> + struct dm_table *map;
>> +
>> + map = dm_get_live_table(md, &srcu_idx);
>> + if (!map) {
>> + DMERR_LIMIT("%s: mapping table unavailable, erroring io",
>> + dm_device_name(md));
>> + dm_put_live_table(md, srcu_idx);
>> + return BLK_STS_IOERR;
>> + }
>> ti = dm_table_find_target(map, 0);
>> dm_put_live_table(md, srcu_idx);
>> }
>> --
>> 2.31.1
>>
>
> I think both dm_submit_bio() and now dm_mq_queue_rq() should _not_
> error the IO. This is such a narrow race during device setup that it
> best to requeue the IO.
>
Yes，make sense, thanks for the fix.
Thanks,
Yi.
> I'll queue this for 5.18:
>
> diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
> index 6948d5db9092..3dd040a56318 100644
> --- a/drivers/md/dm-rq.c
> +++ b/drivers/md/dm-rq.c
> @@ -491,8 +491,13 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
>
> if (unlikely(!ti)) {
> int srcu_idx;
> - struct dm_table *map = dm_get_live_table(md, &srcu_idx);
> + struct dm_table *map;
>
> + map = dm_get_live_table(md, &srcu_idx);
> + if (unlikely(!map)) {
> + dm_put_live_table(md, srcu_idx);
> + return BLK_STS_RESOURCE;
> + }
> ti = dm_table_find_target(map, 0);
> dm_put_live_table(md, srcu_idx);
> }
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 082366d0ad49..c70be6e5ed55 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1533,15 +1533,10 @@ static void dm_submit_bio(struct bio *bio)
> struct dm_table *map;
>
> map = dm_get_live_table(md, &srcu_idx);
> - if (unlikely(!map)) {
> - DMERR_LIMIT("%s: mapping table unavailable, erroring io",
> - dm_device_name(md));
> - bio_io_error(bio);
> - goto out;
> - }
>
> - /* If suspended, queue this IO for later */
> - if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
> + /* If suspended, or map not yet available, queue this IO for later */
> + if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) ||
> + unlikely(!map)) {
> if (bio->bi_opf & REQ_NOWAIT)
> bio_wouldblock_error(bio);
> else if (bio->bi_opf & REQ_RAHEAD)
>
> .
>
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