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@lst.de>
Link: https://lore.kernel.org/r/20230707094239.107968-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 291cf9d..86ff375 100644 (file)
--- 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 4f34525..a582ea0 100644 (file)
--- 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 427e79a..57674b3 100644 (file)
--- 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 */