Hi Coly,
>On 2018/4/16 4:56 PM, tang.junhui@xxxxxxxxxx wrote:
>> 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?
>
>Hi Junhui,
>
>Yes, this is on my pipeline. So far I just want to make a minimal
>change, since the problematic patch is in 4.17 pre-rc1 already. Now this
>patch is under our internal testing already, once the fix is verified, I
>will ask Michael and Jens to pick it as a minor fix.
>
>The changes as you suggested will be a bit larger and not in emergent
>pipe for this moment.
OK, LGTM.
Reviewed-by: Tang Junhui <tang.junhui@xxxxxxxxxx>
Thanks.
Tang Junhui
