From: Steven Rostedt <rostedt@goodmis.org>
To: kernel test robot <lkp@intel.com>
Cc: oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org,
Julia Lawall <Julia.Lawall@inria.fr>
Subject: Re: kernel/trace/ring_buffer.c:412:29-47: WARNING: casting value returned by memory allocation function to (struct buffer_page *) is useless.
Date: Fri, 31 Jul 2026 20:28:04 -0400 [thread overview]
Message-ID: <20260731202804.06a4056f@robin> (raw)
In-Reply-To: <202608010824.vc7vATf0-lkp@intel.com>
On Sat, 01 Aug 2026 08:10:14 +0800
kernel test robot <lkp@intel.com> wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: 8ba098e6b6ff0db8edf28528d1552be261af30d4
> commit: b1e7a590a0133606d3efd41aee38cdeac630b52f ring-buffer: Add helper functions for allocations
> date: 8 months ago
> config: openrisc-randconfig-r062-20260801 (https://download.01.org/0day-ci/archive/20260801/202608010824.vc7vATf0-lkp@intel.com/config)
> compiler: or1k-linux-gcc (GCC) 9.5.0
>
> 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
> | Fixes: b1e7a590a013 ("ring-buffer: Add helper functions for allocations")
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202608010824.vc7vATf0-lkp@intel.com/
>
> cocci warnings: (new ones prefixed by >>)
> >> kernel/trace/ring_buffer.c:412:29-47: WARNING: casting value returned by memory allocation function to (struct buffer_page *) is useless.
> >> kernel/trace/ring_buffer.c:408:31-57: WARNING: casting value returned by memory allocation function to (struct ring_buffer_per_cpu *) is useless.
No, whatever Coccinelle script that reported this is broken.
The typecast is in a macro. The macro is adding the typecast to make
sure that what it is being assigned to is of the proper type.
Hence, it is very *useful*!
-- Steve
>
> vim +412 kernel/trace/ring_buffer.c
>
> 403
> 404 /*
> 405 * For best performance, allocate cpu buffer data cache line sized
> 406 * and per CPU.
> 407 */
> > 408 #define alloc_cpu_buffer(cpu) (struct ring_buffer_per_cpu *) \
> 409 kzalloc_node(ALIGN(sizeof(struct ring_buffer_per_cpu), \
> 410 cache_line_size()), GFP_KERNEL, cpu_to_node(cpu));
> 411
> > 412 #define alloc_cpu_page(cpu) (struct buffer_page *) \
> 413 kzalloc_node(ALIGN(sizeof(struct buffer_page), \
> 414 cache_line_size()), GFP_KERNEL, cpu_to_node(cpu));
> 415
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
prev parent reply other threads:[~2026-08-01 0:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-01 0:10 kernel/trace/ring_buffer.c:412:29-47: WARNING: casting value returned by memory allocation function to (struct buffer_page *) is useless kernel test robot
2026-08-01 0:28 ` Steven Rostedt [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260731202804.06a4056f@robin \
--to=rostedt@goodmis.org \
--cc=Julia.Lawall@inria.fr \
--cc=linux-kernel@vger.kernel.org \
--cc=lkp@intel.com \
--cc=oe-kbuild-all@lists.linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.