block: stack max_user_sectors

The max_user_sectors is one of the three factors determining the actual
max_sectors limit for READ/WRITE requests.  Because of that it needs to
be stacked at least for the device mapper multi-path case where requests
are directly inserted on the lower device.  For SCSI disks this is
important because the sd driver actually sets it's own advisory limit
that is lower than max_hw_sectors based on the block limits VPD page.
While this is a bit odd an unusual, the same effect can happen if a
user or udev script tweaks the value manually.

Fixes: 4f563a64 ("block: add a max_user_discard_sectors queue limit")
Reported-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20240523182618.602003-3-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-settings.c

@@ -611,6 +611,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 	unsigned int top, bottom, alignment, ret = 0;
 
 	t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
+	t->max_user_sectors = min_not_zero(t->max_user_sectors,
+			b->max_user_sectors);
 	t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
 	t->max_dev_sectors = min_not_zero(t->max_dev_sectors, b->max_dev_sectors);
 	t->max_write_zeroes_sectors = min(t->max_write_zeroes_sectors,