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
next prev parent reply other threads:[~2026-08-01 0:28 UTC|newest]
Thread overview: 3+ 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]
2026-08-01 7:05 ` Julia Lawall
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