[PATCH v3] scsi: sd: Fix build warning in sd_revalidate_disk()

[Abinash Singh <abinashsinghlalotra@gmail.com>]

A build warning was triggered due to excessive stack usage in
sd_revalidate_disk():

drivers/scsi/sd.c: In function ‘sd_revalidate_disk.isra’:
drivers/scsi/sd.c:3824:1: warning: the frame size of 1160 bytes is larger than 1024 bytes [-Wframe-larger-than=]

This is caused by a large local struct queue_limits (~400B) allocated
on the stack. Replacing it with a heap allocation using kmalloc()
significantly reduces frame usage. Kernel stack is limited (~8 KB),
and allocating large structs on the stack is discouraged.
As the function already performs heap allocations (e.g. for buffer),
this change fits well.

Signed-off-by: Abinash Singh <abinashsinghlalotra@gmail.com>
---

Hi ,

As I mentioned in v2,.. this is the corresponding
v3 of that. Only difference is in using __free() attribute
Please infor  me which one is better.

changelog v2->v3:
	used __free(kfree) attribute.
	no extra goto statements (i.e `free_lim`)

lim was initialized to NULL because there is a return path
before its allocation. Early exit will pass uninitlized pointer to
`kfree`.
We could move the allocation earlier, before this check:

			if (!scsi_device_online(sdp))
    			goto out;
However, doing so would result in unnecessary allocation
if the device is not online, leading to wasted resources.

Thanks,
---
 drivers/scsi/sd.c | 42 +++++++++++++++++++++++++-----------------
 1 file changed, 25 insertions(+), 17 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 4a68b2ab2804..50abbab7e27a 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -34,6 +34,7 @@
  */
 
 #include <linux/bio-integrity.h>
+#include <linux/cleanup.h>
 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/kernel.h>
@@ -3696,7 +3697,7 @@ static int sd_revalidate_disk(struct gendisk *disk)
 	struct scsi_disk *sdkp = scsi_disk(disk);
 	struct scsi_device *sdp = sdkp->device;
 	sector_t old_capacity = sdkp->capacity;
-	struct queue_limits lim;
+	struct queue_limits *lim __free(kfree) = NULL;
 	unsigned char *buffer;
 	unsigned int dev_max;
 	int err;
@@ -3711,6 +3712,13 @@ static int sd_revalidate_disk(struct gendisk *disk)
 	if (!scsi_device_online(sdp))
 		goto out;
 
+	lim = kmalloc(sizeof(*lim), GFP_KERNEL);
+	if (!lim) {
+		sd_printk(KERN_WARNING, sdkp,
+			"sd_revalidate_disk: Disk limit allocation failure.\n");
+		goto out;
+	}
+
 	buffer = kmalloc(SD_BUF_SIZE, GFP_KERNEL);
 	if (!buffer) {
 		sd_printk(KERN_WARNING, sdkp, "sd_revalidate_disk: Memory "
@@ -3720,14 +3728,14 @@ static int sd_revalidate_disk(struct gendisk *disk)
 
 	sd_spinup_disk(sdkp);
 
-	lim = queue_limits_start_update(sdkp->disk->queue);
+	*lim = queue_limits_start_update(sdkp->disk->queue);
 
 	/*
 	 * Without media there is no reason to ask; moreover, some devices
 	 * react badly if we do.
 	 */
 	if (sdkp->media_present) {
-		sd_read_capacity(sdkp, &lim, buffer);
+		sd_read_capacity(sdkp, lim, buffer);
 		/*
 		 * Some USB/UAS devices return generic values for mode pages
 		 * until the media has been accessed. Trigger a READ operation
@@ -3741,17 +3749,17 @@ static int sd_revalidate_disk(struct gendisk *disk)
 		 * cause this to be updated correctly and any device which
 		 * doesn't support it should be treated as rotational.
 		 */
-		lim.features |= (BLK_FEAT_ROTATIONAL | BLK_FEAT_ADD_RANDOM);
+		lim->features |= (BLK_FEAT_ROTATIONAL | BLK_FEAT_ADD_RANDOM);
 
 		if (scsi_device_supports_vpd(sdp)) {
 			sd_read_block_provisioning(sdkp);
-			sd_read_block_limits(sdkp, &lim);
+			sd_read_block_limits(sdkp, lim);
 			sd_read_block_limits_ext(sdkp);
-			sd_read_block_characteristics(sdkp, &lim);
-			sd_zbc_read_zones(sdkp, &lim, buffer);
+			sd_read_block_characteristics(sdkp, lim);
+			sd_zbc_read_zones(sdkp, lim, buffer);
 		}
 
-		sd_config_discard(sdkp, &lim, sd_discard_mode(sdkp));
+		sd_config_discard(sdkp, lim, sd_discard_mode(sdkp));
 
 		sd_print_capacity(sdkp, old_capacity);
 
@@ -3761,45 +3769,45 @@ static int sd_revalidate_disk(struct gendisk *disk)
 		sd_read_app_tag_own(sdkp, buffer);
 		sd_read_write_same(sdkp, buffer);
 		sd_read_security(sdkp, buffer);
-		sd_config_protection(sdkp, &lim);
+		sd_config_protection(sdkp, lim);
 	}
 
 	/*
 	 * We now have all cache related info, determine how we deal
 	 * with flush requests.
 	 */
-	sd_set_flush_flag(sdkp, &lim);
+	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;
 
 	/* Some devices report a maximum block count for READ/WRITE requests. */
 	dev_max = min_not_zero(dev_max, sdkp->max_xfer_blocks);
-	lim.max_dev_sectors = logical_to_sectors(sdp, dev_max);
+	lim->max_dev_sectors = logical_to_sectors(sdp, dev_max);
 
 	if (sd_validate_min_xfer_size(sdkp))
-		lim.io_min = logical_to_bytes(sdp, sdkp->min_xfer_blocks);
+		lim->io_min = logical_to_bytes(sdp, sdkp->min_xfer_blocks);
 	else
-		lim.io_min = 0;
+		lim->io_min = 0;
 
 	/*
 	 * Limit default to SCSI host optimal sector limit if set. There may be
 	 * an impact on performance for when the size of a request exceeds this
 	 * host limit.
 	 */
-	lim.io_opt = sdp->host->opt_sectors << SECTOR_SHIFT;
+	lim->io_opt = sdp->host->opt_sectors << SECTOR_SHIFT;
 	if (sd_validate_opt_xfer_size(sdkp, dev_max)) {
-		lim.io_opt = min_not_zero(lim.io_opt,
+		lim->io_opt = min_not_zero(lim->io_opt,
 				logical_to_bytes(sdp, sdkp->opt_xfer_blocks));
 	}
 
 	sdkp->first_scan = 0;
 
 	set_capacity_and_notify(disk, logical_to_sectors(sdp, sdkp->capacity));
-	sd_config_write_same(sdkp, &lim);
+	sd_config_write_same(sdkp, lim);
 	kfree(buffer);
 
-	err = queue_limits_commit_update_frozen(sdkp->disk->queue, &lim);
+	err = queue_limits_commit_update_frozen(sdkp->disk->queue, lim);
 	if (err)
 		return err;
 
-- 
2.50.1