linux-kernel - Re: arch/alpha/include/asm/rwonce.h:25:35: warning: array subscript 0 is outside array bounds of 'struct inode[11885788707287082]'

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Message-ID: <CAOQ4uxjTv+5cB4z8TZQ02c5F3rags1HARoEQG9834A0+_+_twA@mail.gmail.com>
Date:   Wed, 20 Sep 2023 07:35:23 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     kernel test robot <lkp@...el.com>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Alexander Larsson <alexl@...hat.com>,
        Miklos Szeredi <mszeredi@...hat.com>
Subject: Re: arch/alpha/include/asm/rwonce.h:25:35: warning: array subscript 0
 is outside array bounds of 'struct inode[11885788707287082]'

On Tue, Sep 19, 2023 at 1:43 PM kernel test robot <lkp@...el.com> wrote:
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   2cf0f715623872823a72e451243bbf555d10d032
> commit: 0af950f57fefabab628f1963af881e6b9bfe7f38 ovl: move ovl_entry into ovl_inode

Are you sure that this is the regressing commit?
I don't see anything that has changed wrt the ovl_dentry_upper()
call chain.

> date:   3 months ago
> config: alpha-allyesconfig (https://download.01.org/0day-ci/archive/20230919/202309191848.cMwd2D4d-lkp@intel.com/config)
> compiler: alpha-linux-gcc (GCC) 13.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230919/202309191848.cMwd2D4d-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202309191848.cMwd2D4d-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
>    In file included from include/linux/compiler.h:246,
>                     from include/linux/build_bug.h:5,
>                     from include/linux/container_of.h:5,
>                     from include/linux/list.h:5,
>                     from include/linux/wait.h:7,
>                     from include/linux/wait_bit.h:8,
>                     from include/linux/fs.h:6,
>                     from fs/overlayfs/util.c:7:
>    In function 'ovl_upperdentry_dereference',
>        inlined from 'ovl_dentry_upper' at fs/overlayfs/util.c:266:9,
>        inlined from 'ovl_path_type' at fs/overlayfs/util.c:184:6:
> >> arch/alpha/include/asm/rwonce.h:25:35: warning: array subscript 0 is outside array bounds of 'struct inode[11885788707287082]' [-Warray-bounds=]
>       25 |         __unqual_scalar_typeof(x) __x =                                 \
>          |                                   ^~~
>    include/asm-generic/rwonce.h:50:9: note: in expansion of macro '__READ_ONCE'
>       50 |         __READ_ONCE(x);                                                 \
>          |         ^~~~~~~~~~~
>    fs/overlayfs/ovl_entry.h:163:16: note: in expansion of macro 'READ_ONCE'
>      163 |         return READ_ONCE(oi->__upperdentry);
>          |                ^~~~~~~~~
>

Why would the type of oi->__upperdentry be considered to be
'struct inode[11885788707287082]'?
I don't understand this report.

Miklos, any clue?

Thanks,
Amir.

>
> vim +25 arch/alpha/include/asm/rwonce.h
>
> d6462858851549 Will Deacon 2019-10-30  11
> d6462858851549 Will Deacon 2019-10-30  12  /*
> d6462858851549 Will Deacon 2019-10-30  13   * Alpha is apparently daft enough to reorder address-dependent loads
> d6462858851549 Will Deacon 2019-10-30  14   * on some CPU implementations. Knock some common sense into it with
> d6462858851549 Will Deacon 2019-10-30  15   * a memory barrier in READ_ONCE().
> d6462858851549 Will Deacon 2019-10-30  16   *
> d6462858851549 Will Deacon 2019-10-30  17   * For the curious, more information about this unusual reordering is
> d6462858851549 Will Deacon 2019-10-30  18   * available in chapter 15 of the "perfbook":
> d6462858851549 Will Deacon 2019-10-30  19   *
> d6462858851549 Will Deacon 2019-10-30  20   *  https://kernel.org/pub/linux/kernel/people/paulmck/perfbook/perfbook.html
> d6462858851549 Will Deacon 2019-10-30  21   *
> d6462858851549 Will Deacon 2019-10-30  22   */
> d6462858851549 Will Deacon 2019-10-30  23  #define __READ_ONCE(x)                                                       \
> d6462858851549 Will Deacon 2019-10-30  24  ({                                                                   \
> d6462858851549 Will Deacon 2019-10-30 @25       __unqual_scalar_typeof(x) __x =                                 \
> d6462858851549 Will Deacon 2019-10-30  26               (*(volatile typeof(__x) *)(&(x)));                      \
> d6462858851549 Will Deacon 2019-10-30  27       mb();                                                           \
> d6462858851549 Will Deacon 2019-10-30  28       (typeof(x))__x;                                                 \
> d6462858851549 Will Deacon 2019-10-30  29  })
> d6462858851549 Will Deacon 2019-10-30  30
>
> :::::: The code at line 25 was first introduced by commit
> :::::: d6462858851549c62d73eaa14b31132b0f32d6b6 alpha: Override READ_ONCE() with barriered implementation
>
> :::::: TO: Will Deacon <will@...nel.org>
> :::::: CC: Will Deacon <will@...nel.org>
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki