linux-kernel - Re: [PATCH] Revert "md: raid1: use bio helper in process

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Message-ID: <CACVXFVNzGV+P9CXcyqcV0_rJVM9F7dOR3_aX2xv0GQTsMaXX6A@mail.gmail.com>
Date:   Tue, 28 Mar 2017 19:42:44 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Shaohua Li <shli@...nel.org>, NeilBrown <neilb@...e.com>,
        Jens Axboe <axboe@...com>, "colyli@...e.de" <colyli@...e.de>,
        Guoqing Jiang <gqjiang@...e.com>,
        Mike Christie <mchristi@...hat.com>,
        "open list:SOFTWARE RAID (Multiple Disks) SUPPORT" 
        <linux-raid@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "md: raid1: use bio helper in process_checks()"

On Tue, Mar 28, 2017 at 7:35 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Tue, Mar 28, 2017 at 12:44 PM, Ming Lei <tom.leiming@...il.com> wrote:
>> On Tue, Mar 28, 2017 at 5:49 PM, Arnd Bergmann <arnd@...db.de> wrote:
>>> Commit 60928a91b0b3 ("md: raid1: use bio helper in process_checks()")
>>> is probably correct, but I get a new compile-time warning after
>>> it, and have trouble understanding what it fixes:
>>>
>>> drivers/md/raid1.c: In function 'sync_request_write':
>>> drivers/md/raid1.c:2172:9: error: 'page_len$' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>>>      if (memcmp(page_address(ppages[j]),
>>>          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>          page_address(spages[j]),
>>>          ~~~~~~~~~~~~~~~~~~~~~~~~
>>>          page_len[j]))
>>>          ~~~~~~~~~~~~
>>> drivers/md/raid1.c:2160:7: note: 'page_len$' was declared here
>>>    int page_len[RESYNC_PAGES];
>>>        ^~~~~~~~
>>>
>>> This reverts it to resolve the warning.
>>
>> Please try the following patch:
>>
>>  https://lkml.org/lkml/2017/3/28/126
>
>
> That patch will certainly shut up the warning, but will also prevent
> the compiler from warning when the function gets changed in some
> way that actually leads to an uninitialized use of the page_len array,

Why do you think that it leads to an uninitialized use of the page_len array?

The following code does initialize the array well enough for future use:

               bio_for_each_segment_all(bi, sbio, j)
                       page_len[j] = bi->bv_len;

That is why we don't need to initialize the array explicitly, but just
for killing
the warning.


Thanks,
Ming Lei