On 2018/8/11 2:19 AM, Jens Axboe wrote:

On 8/10/18 9:45 AM, Coly Li wrote:

quoted

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 <redacted>
Cc: stable@vger.kernel.org #4.16+
Cc: Kai Krakow <redacted>
Cc: Stefan Priebe <redacted>

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.

Also, the fixes line should be:

Fixes: ea8c5356d390 ("bcache: set max writeback rate when I/O request is idle")

(no Commit). I missed that on some of your earlier commits.

Copied, keep in mind for next time.

Applied with those edits, and some wording changes.

Thanks for your help !

Coly Li