bcache: store disk name in struct cache and struct cached_dev

Current code uses bdevname() or bio_devname() to reference gendisk
disk name when bcache needs to display the disk names in kernel message.
It was safe before bcache device failure handling patch set merged in,
because when devices are failed, there was deadlock to prevent bcache
printing error messages with gendisk disk name. But after the failure
handling patch set merged, the deadlock is fixed, so it is possible
that the gendisk structure bdev->hd_disk is released when bdevname() is
called to reference bdev->bd_disk->disk_name[]. This is why I receive
bug report of NULL pointers deference panic.

This patch stores gendisk disk name in a buffer inside struct cache and
struct cached_dev, then print out the offline device name won't reference
bdev->hd_disk anymore. And this patch also avoids extra function calls
of bdevname() and bio_devnmae().

Changelog:
v3, add Reviewed-by from Hannes.
v2, call bdevname() earlier in register_bdev()
v1, first version with segguestion from Junhui Tang.

Fixes: c7b7bd07404c5 ("bcache: add io_disable to struct cached_dev")
Fixes: 5138ac6748e38 ("bcache: fix misleading error message in bch_count_io_errors()")
Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 3 insertions, 5 deletions

diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
index 7fac97ae036e..2ddf8515e6a5 100644
--- a/drivers/md/bcache/io.c
+++ b/drivers/md/bcache/io.c
@@ -52,7 +52,6 @@ void bch_submit_bbio(struct bio *bio, struct cache_set *c,
 /* IO errors */
 void bch_count_backing_io_errors(struct cached_dev *dc, struct bio *bio)
 {
-	char buf[BDEVNAME_SIZE];
 	unsigned errors;
 
 	WARN_ONCE(!dc, "NULL pointer of struct cached_dev");
@@ -60,7 +59,7 @@ void bch_count_backing_io_errors(struct cached_dev *dc, struct bio *bio)
 	errors = atomic_add_return(1, &dc->io_errors);
 	if (errors < dc->error_limit)
 		pr_err("%s: IO error on backing device, unrecoverable",
-			bio_devname(bio, buf));
+			dc->backing_dev_name);
 	else
 		bch_cached_dev_error(dc);
 }
@@ -105,19 +104,18 @@ void bch_count_io_errors(struct cache *ca,
 	}
 
 	if (error) {
-		char buf[BDEVNAME_SIZE];
 		unsigned errors = atomic_add_return(1 << IO_ERROR_SHIFT,
 						    &ca->io_errors);
 		errors >>= IO_ERROR_SHIFT;
 
 		if (errors < ca->set->error_limit)
 			pr_err("%s: IO error on %s%s",
-			       bdevname(ca->bdev, buf), m,
+			       ca->cache_dev_name, m,
 			       is_read ? ", recovering." : ".");
 		else
 			bch_cache_set_error(ca->set,
 					    "%s: too many IO errors %s",
-					    bdevname(ca->bdev, buf), m);
+					    ca->cache_dev_name, m);
 	}
 }