block: move cache control settings out of queue->flags

Move the cache control settings into the queue_limits so that the flags
can be set atomically with the device queue frozen.

Add new features and flags field for the driver set flags, and internal
(usually sysfs-controlled) flags in the block layer.  Note that we'll
eventually remove enough field from queue_limits to bring it back to the
previous size.

The disable flag is inverted compared to the previous meaning, which
means it now survives a rescan, similar to the max_sectors and
max_discard_sectors user limits.

The FLUSH and FUA flags are now inherited by blk_stack_limits, which
simplified the code in dm a lot, but also causes a slight behavior
change in that dm-switch and dm-unstripe now advertise a write cache
despite setting num_flush_bios to 0.  The I/O path will handle this
gracefully, but as far as I can tell the lack of num_flush_bios
and thus flush support is a pre-existing data integrity bug in those
targets that really needs fixing, after which a non-zero num_flush_bios
should be required in dm for targets that map to underlying devices.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20240617060532.127975-14-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 19 insertions, 9 deletions

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 66f7d1e3429c..d8ee4a4d4a62 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -120,17 +120,18 @@ static const char *sd_cache_types[] = {
 	"write back, no read (daft)"
 };
 
-static void sd_set_flush_flag(struct scsi_disk *sdkp)
+static void sd_set_flush_flag(struct scsi_disk *sdkp,
+		struct queue_limits *lim)
 {
-	bool wc = false, fua = false;
-
 	if (sdkp->WCE) {
-		wc = true;
+		lim->features |= BLK_FEAT_WRITE_CACHE;
 		if (sdkp->DPOFUA)
-			fua = true;
+			lim->features |= BLK_FEAT_FUA;
+		else
+			lim->features &= ~BLK_FEAT_FUA;
+	} else {
+		lim->features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA);
 	}
-
-	blk_queue_write_cache(sdkp->disk->queue, wc, fua);
 }
 
 static ssize_t
@@ -168,9 +169,18 @@ cache_type_store(struct device *dev, struct device_attribute *attr,
 	wce = (ct & 0x02) && !sdkp->write_prot ? 1 : 0;
 
 	if (sdkp->cache_override) {
+		struct queue_limits lim;
+
 		sdkp->WCE = wce;
 		sdkp->RCD = rcd;
-		sd_set_flush_flag(sdkp);
+
+		lim = queue_limits_start_update(sdkp->disk->queue);
+		sd_set_flush_flag(sdkp, &lim);
+		blk_mq_freeze_queue(sdkp->disk->queue);
+		ret = queue_limits_commit_update(sdkp->disk->queue, &lim);
+		blk_mq_unfreeze_queue(sdkp->disk->queue);
+		if (ret)
+			return ret;
 		return count;
 	}
 
@@ -3663,7 +3673,7 @@ static int sd_revalidate_disk(struct gendisk *disk)
 	 * We now have all cache related info, determine how we deal
 	 * with flush requests.
 	 */
-	sd_set_flush_flag(sdkp);
+	sd_set_flush_flag(sdkp, &lim);
 
 	/* Initial block count limit based on CDB TRANSFER LENGTH field size. */
 	dev_max = sdp->use_16_for_rw ? SD_MAX_XFER_BLOCKS : SD_DEF_XFER_BLOCKS;