On 8/10/18 10:49 PM, Coly Li wrote:
> On 2018/8/11 2:19 AM, Jens Axboe wrote:
>> On 8/10/18 9:45 AM, Coly Li wrote:
>>> Commit ea8c5356d390 ("bcache: set max writeback rate when I/O request
>>> is idle") changes struct bch_ratelimit member rate from uint32_t to
>>> atomic_long_t and uses atomic_long_set() in drivers/md/bcache/sysfs.c
>>> to set new writeback rate, after the input is converted from memory
>>> buf to long int by sysfs_strtoul_clamp().
>>>
>>> The above change has a problem because there is an implicit return
>>> inside sysfs_strtoul_clamp() so the following atomic_long_set()
>>> won't be called. This error is detected by 0day system with following
>>> snipped smatch warnings:
>>>
>>> drivers/md/bcache/sysfs.c:271 __cached_dev_store() error: uninitialized
>>> symbol 'v'.
>>> 270 sysfs_strtoul_clamp(writeback_rate, v, 1, INT_MAX);
>>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> @271 atomic_long_set(&dc->writeback_rate.rate, v);
>>>
>>> This patch fixes the above error by using strtoul_safe_clamp() to
>>> convert the input buffer into a long int type result.
>>>
>>> Fixes: Commit ea8c5356d390 ("bcache: set max writeback rate when I/O request is idle")
>>> Signed-off-by: Coly Li <colyli@xxxxxxx>
>>> Cc: stable@xxxxxxxxxxxxxxx #4.16+
>>> Cc: Kai Krakow <kai@xxxxxxxxxxx>
>>> Cc: Stefan Priebe <s.priebe@xxxxxxxxxxxx>
>>
>
> Hi Jens,
>
>> You don't need to CC stable for this, the commit isn't in a released kernel
>> yet. In fact, it's not even in Linus's tree, it's just queued up for 4.19.
>>
>
> What I thought was, Commit ea8c5356d390 ("bcache: set max writeback rate
> when I/O request is idle") is a stable fix, so this patch should go into
> stable as well. Otherwise the stable kernel cannot manually set
> writeback_rate via sysfs interface.
It's not necessary when new patch is correctly marked as fixing one that
is going to stable.
--
Jens Axboe
