netdev - Re: [PATCH net 07/18] net/ena: refactor ena_get

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Date:   Tue, 22 Nov 2016 00:23:48 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Netanel Belgazal <netanel@...apurnalabs.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        davem@...emloft.net, netdev@...r.kernel.org,
        Netanel Belgazal <netanel@...apurnalabs.com>, dwmw@...zon.com,
        zorik@...apurnalabs.com, alex@...apurnalabs.com,
        saeed@...apurnalabs.com, msw@...zon.com, aliguori@...zon.com,
        nafea@...apurnalabs.com
Subject: Re: [PATCH net 07/18] net/ena: refactor ena_get_stats64 to be atomic
 context safe

Hi Netanel,

[auto build test WARNING on net/master]

url:    https://github.com/0day-ci/linux/commits/Netanel-Belgazal/Update-ENA-driver-to-version-1-1-2/20161120-165649
config: i386-randconfig-h1-11212236 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   In file included from include/linux/mmzone.h:15:0,
                    from include/linux/gfp.h:5,
                    from include/linux/cpu_rmap.h:14,
                    from drivers/net/ethernet/amazon/ena/ena_netdev.c:36:
   drivers/net/ethernet/amazon/ena/ena_netdev.c: In function 'ena_get_stats64':
>> include/linux/seqlock.h:204:19: warning: 'rx_ring' may be used uninitialized in this function [-Wmaybe-uninitialized]
     return unlikely(s->sequence != start);
                      ^~
   drivers/net/ethernet/amazon/ena/ena_netdev.c:2188:19: note: 'rx_ring' was declared here
     struct ena_ring *rx_ring, *tx_ring;
                      ^~~~~~~

vim +/rx_ring +204 include/linux/seqlock.h

4f988f15 Linus Torvalds 2012-05-04  188  /**
3c22cd57 Nick Piggin    2011-01-07  189   * __read_seqcount_retry - end a seq-read critical section (without barrier)
3c22cd57 Nick Piggin    2011-01-07  190   * @s: pointer to seqcount_t
3c22cd57 Nick Piggin    2011-01-07  191   * @start: count, from read_seqcount_begin
3c22cd57 Nick Piggin    2011-01-07  192   * Returns: 1 if retry is required, else 0
3c22cd57 Nick Piggin    2011-01-07  193   *
3c22cd57 Nick Piggin    2011-01-07  194   * __read_seqcount_retry is like read_seqcount_retry, but has no smp_rmb()
3c22cd57 Nick Piggin    2011-01-07  195   * barrier. Callers should ensure that smp_rmb() or equivalent ordering is
3c22cd57 Nick Piggin    2011-01-07  196   * provided before actually loading any of the variables that are to be
3c22cd57 Nick Piggin    2011-01-07  197   * protected in this critical section.
3c22cd57 Nick Piggin    2011-01-07  198   *
3c22cd57 Nick Piggin    2011-01-07  199   * Use carefully, only in critical code, and comment how the barrier is
3c22cd57 Nick Piggin    2011-01-07  200   * provided.
3c22cd57 Nick Piggin    2011-01-07  201   */
3c22cd57 Nick Piggin    2011-01-07  202  static inline int __read_seqcount_retry(const seqcount_t *s, unsigned start)
3c22cd57 Nick Piggin    2011-01-07  203  {
3c22cd57 Nick Piggin    2011-01-07 @204  	return unlikely(s->sequence != start);
3c22cd57 Nick Piggin    2011-01-07  205  }
3c22cd57 Nick Piggin    2011-01-07  206  
3c22cd57 Nick Piggin    2011-01-07  207  /**
3c22cd57 Nick Piggin    2011-01-07  208   * read_seqcount_retry - end a seq-read critical section
3c22cd57 Nick Piggin    2011-01-07  209   * @s: pointer to seqcount_t
3c22cd57 Nick Piggin    2011-01-07  210   * @start: count, from read_seqcount_begin
3c22cd57 Nick Piggin    2011-01-07  211   * Returns: 1 if retry is required, else 0
3c22cd57 Nick Piggin    2011-01-07  212   *

:::::: The code at line 204 was first introduced by commit
:::::: 3c22cd5709e8143444a6d08682a87f4c57902df3 kernel: optimise seqlock

:::::: TO: Nick Piggin <npiggin@...nel.dk>
:::::: CC: Nick Piggin <npiggin@...nel.dk>

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