Hi Coly,
>When backing device is offline, memory object pointed by dc->bdev might be
>released in some condititions. I have bug report that bdevname() triggers
>a NULL pointer deference panic inside bch_cached_dev_error(), where
>dc->bdev is NULL.
>
>This patch adds char backing_dev_name[BDEVNAME_SIZE] in struct cached_dev,
>and stored backing device name in backing_dev_nmae during backing device
>registration. Then when backing device is offline, pr_err() can still
>print message with backing device name without calling bdevname(). And
>backing_dev_name is also helpful when debugging crash code.
>
>Fixes: c7b7bd07404c ("bcache: add io_disable to struct cached_dev")
>Signed-off-by: Coly Li <colyli@xxxxxxx>
>---
> drivers/md/bcache/bcache.h | 2 ++
> drivers/md/bcache/super.c | 10 ++++------
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
>index d338b7086013..9af0ad7f6243 100644
>--- a/drivers/md/bcache/bcache.h
>+++ b/drivers/md/bcache/bcache.h
>@@ -392,6 +392,8 @@ struct cached_dev {
> #define DEFAULT_CACHED_DEV_ERROR_LIMIT 64
> atomic_t io_errors;
> unsigned error_limit;
>+
>+ char backing_dev_name[BDEVNAME_SIZE];
> };
>
> enum alloc_reserve {
>diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>index d90d9e59ca00..f2512e3e67e6 100644
>--- a/drivers/md/bcache/super.c
>+++ b/drivers/md/bcache/super.c
>@@ -1225,13 +1225,13 @@ static void register_bdev(struct cache_sb *sb, struct page *sb_page,
> struct block_device *bdev,
> struct cached_dev *dc)
> {
>- char name[BDEVNAME_SIZE];
> const char *err = "cannot allocate memory";
> struct cache_set *c;
>
> memcpy(&dc->sb, sb, sizeof(struct cache_sb));
> dc->bdev = bdev;
> dc->bdev->bd_holder = dc;
>+ bdevname(bdev, dc->backing_dev_name);
>
> bio_init(&dc->sb_bio, dc->sb_bio.bi_inline_vecs, 1);
> bio_first_bvec_all(&dc->sb_bio)->bv_page = sb_page;
>@@ -1247,7 +1247,7 @@ static void register_bdev(struct cache_sb *sb, struct page *sb_page,
> if (bch_cache_accounting_add_kobjs(&dc->accounting, &dc->disk.kobj))
> goto err;
>
>- pr_info("registered backing device %s", bdevname(bdev, name));
>+ pr_info("registered backing device %s", dc->backing_dev_name);
>
> list_add(&dc->list, &uncached_devices);
> list_for_each_entry(c, &bch_cache_sets, list)
>@@ -1259,7 +1259,7 @@ static void register_bdev(struct cache_sb *sb, struct page *sb_page,
>
> return;
> err:
>- pr_notice("error %s: %s", bdevname(bdev, name), err);
>+ pr_notice("error %s: %s", dc->backing_dev_name, err);
> bcache_device_stop(&dc->disk);
> }
>
>@@ -1367,8 +1367,6 @@ int bch_flash_dev_create(struct cache_set *c, uint64_t size)
>
> bool bch_cached_dev_error(struct cached_dev *dc)
> {
>- char name[BDEVNAME_SIZE];
>-
> if (!dc || test_bit(BCACHE_DEV_CLOSING, &dc->disk.flags))
> return false;
>
>@@ -1377,7 +1375,7 @@ bool bch_cached_dev_error(struct cached_dev *dc)
> smp_mb();
>
> pr_err("stop %s: too many IO errors on backing device %s\n",
>- dc->disk.disk->disk_name, bdevname(dc->bdev, name));
>+ dc->disk.disk->disk_name, dc->backing_dev_name);
>
> bcache_device_stop(&dc->disk);
> return true;
>--
>2.16.2
Since you have wrote it in dc->backing_dev_name, could you change all
bdevname(dc->bdev, buf) into dc->backing_dev_name in bcache?
Thanks.
Tang Junhui
