Hi,
在 2025/07/22 9:07, Damien Le Moal 写道:
On 7/21/25 11:04 PM, Nilay Shroff wrote:
When setting up a null block device, we initialize a tagset that
includes a driver_data field—typically used by block drivers to
store a pointer to driver-specific data. In the case of null_blk,
this should point to the struct nullb instance.
However, due to recent tagset refactoring in the null_blk driver, we
missed initializing driver_data when creating a shared tagset. As a
result, software queues (ctx) fail to map correctly to new hardware
queues (hctx). For example, increasing the number of submit queues
triggers an nr_hw_queues update, which invokes null_map_queues() to
remap queues. Since set->driver_data is unset, null_map_queues()
fails to map any ctx to the new hctxs, leading to hctx->nr_ctx == 0,
effectively making the hardware queues unusable for I/O.
I don't get it, for the case shared tagset, g_submit_queues and
g_poll_queues should be used, how can you increasing submit_queues?
This patch fixes the issue by ensuring that set->driver_data is properly
initialized to point to the struct nullb during tagset setup.
Fixes: 72ca28765fc4 ("null_blk: refactor tag_set setup")
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
Signed-off-by: Nilay Shroff <nilay@xxxxxxxxxxxxx>
---
drivers/block/null_blk/main.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index aa163ae9b2aa..fbae0427263d 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -1856,6 +1856,7 @@ static int null_setup_tagset(struct nullb *nullb)
{
if (nullb->dev->shared_tags) {
nullb->tag_set = &tag_set;
+ nullb->tag_set->driver_data = nullb;
This looks better, but in the end, why is this even needed ? Since this is a
shared tagset, multiple nullb devices can use that same tagset, so setting the
driver_data pointer to this device only seems incorrect.
Yes this looks incorrect, if there are multiple null_dev shared one
tag_set and blk_mq_update_nr_hw_queues() is triggered, all null_dev will
end up accesing the same null_dev in the map_queues callback.
Checking the code, the only function that makes use of this pointer is
null_map_queues(), which correctly test for private_data being NULL.
So why do we need this ? Isn't your patch 1/2 enough to fix the crash you got ?
Same question :)
Thanks,
Kuai
return null_init_global_tag_set();
}
