block: retry call probe after request_module in blk_request_module

Set kernel config:

 CONFIG_BLK_DEV_LOOP=m
 CONFIG_BLK_DEV_LOOP_MIN_COUNT=0

Do latter:

 mknod loop0 b 7 0
 exec 4<> loop0

Before commit e418de3abcda ("block: switch gendisk lookup to a simple
xarray"), lookup_gendisk will first use base_probe to load module loop,
and then the retry will call loop_probe to prepare the loop disk. Finally
open for this disk will success. However, after this commit, we lose the
retry logic, and open will fail with ENXIO. Block device autoloading is
deprecated and will be removed soon, but maybe we should keep open success
until we really remove it. So, give a retry to fix it.

Fixes: e418de3abcda ("block: switch gendisk lookup to a simple xarray")
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Yang Erkun <yangerkun@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241209110435.3670985-1-yangerkun@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/genhd.c b/block/genhd.c
index 5678194b6b1a1bd38e7259ebe0e7b7cf05689582..5da3c9a64e643251fce1944a58f17fcc14238074 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -797,7 +797,7 @@ static ssize_t disk_badblocks_store(struct device *dev,
 }
 
 #ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
-void blk_request_module(dev_t devt)
+static bool blk_probe_dev(dev_t devt)
 {
        unsigned int major = MAJOR(devt);
        struct blk_major_name **n;
@@ -807,14 +807,26 @@ void blk_request_module(dev_t devt)
                if ((*n)->major == major && (*n)->probe) {
                        (*n)->probe(devt);
                        mutex_unlock(&major_names_lock);
-                       return;
+                       return true;
                }
        }
        mutex_unlock(&major_names_lock);
+       return false;
+}
+
+void blk_request_module(dev_t devt)
+{
+       int error;
+
+       if (blk_probe_dev(devt))
+               return;
 
-       if (request_module("block-major-%d-%d", MAJOR(devt), MINOR(devt)) > 0)
-               /* Make old-style 2.4 aliases work */
-               request_module("block-major-%d", MAJOR(devt));
+       error = request_module("block-major-%d-%d", MAJOR(devt), MINOR(devt));
+       /* Make old-style 2.4 aliases work */
+       if (error > 0)
+               error = request_module("block-major-%d", MAJOR(devt));
+       if (!error)
+               blk_probe_dev(devt);
 }
 #endif /* CONFIG_BLOCK_LEGACY_AUTOLOAD */