Patch "block: don't allow enabling a cache on devices that don't support it" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    block: don't allow enabling a cache on devices that don't support it

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     block-don-t-allow-enabling-a-cache-on-devices-that-d.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1a6827900830ea949779145d93e043653f27cac9
Author: Christoph Hellwig <hch@xxxxxx>
Date:   Fri Jul 7 11:42:39 2023 +0200

    block: don't allow enabling a cache on devices that don't support it
    
    [ Upstream commit 43c9835b144c7ce29efe142d662529662a9eb376 ]
    
    Currently the write_cache attribute allows enabling the QUEUE_FLAG_WC
    flag on devices that never claimed the capability.
    
    Fix that by adding a QUEUE_FLAG_HW_WC flag that is set by
    blk_queue_write_cache and guards re-enabling the cache through sysfs.
    
    Note that any rescan that calls blk_queue_write_cache will still
    re-enable the write cache as in the current code.
    
    Fixes: 93e9d8e836cb ("block: add ability to flag write back caching on a device")
    Signed-off-by: Christoph Hellwig <hch@xxxxxx>
    Link: https://lore.kernel.org/r/20230707094239.107968-3-hch@xxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 291cf9df7fc29..86ff375c00ce4 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -824,10 +824,13 @@ EXPORT_SYMBOL(blk_set_queue_depth);
  */
 void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
 {
-	if (wc)
+	if (wc) {
+		blk_queue_flag_set(QUEUE_FLAG_HW_WC, q);
 		blk_queue_flag_set(QUEUE_FLAG_WC, q);
-	else
+	} else {
+		blk_queue_flag_clear(QUEUE_FLAG_HW_WC, q);
 		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
+	}
 	if (fua)
 		blk_queue_flag_set(QUEUE_FLAG_FUA, q);
 	else
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 4f34525bafac7..a582ea0da74f5 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -528,13 +528,16 @@ static ssize_t queue_wc_show(struct request_queue *q, char *page)
 static ssize_t queue_wc_store(struct request_queue *q, const char *page,
 			      size_t count)
 {
-	if (!strncmp(page, "write back", 10))
+	if (!strncmp(page, "write back", 10)) {
+		if (!test_bit(QUEUE_FLAG_HW_WC, &q->queue_flags))
+			return -EINVAL;
 		blk_queue_flag_set(QUEUE_FLAG_WC, q);
-	else if (!strncmp(page, "write through", 13) ||
-		 !strncmp(page, "none", 4))
+	} else if (!strncmp(page, "write through", 13) ||
+		 !strncmp(page, "none", 4)) {
 		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
-	else
+	} else {
 		return -EINVAL;
+	}
 
 	return count;
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 427e79ac72194..57674b3c58774 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -565,6 +565,7 @@ struct request_queue {
 #define QUEUE_FLAG_NOXMERGES	9	/* No extended merges */
 #define QUEUE_FLAG_ADD_RANDOM	10	/* Contributes to random pool */
 #define QUEUE_FLAG_SAME_FORCE	12	/* force complete on same CPU */
+#define QUEUE_FLAG_HW_WC	18	/* Write back caching supported */
 #define QUEUE_FLAG_INIT_DONE	14	/* queue is initialized */
 #define QUEUE_FLAG_STABLE_WRITES 15	/* don't modify blks until WB is done */
 #define QUEUE_FLAG_POLL		16	/* IO polling enabled if set */