linux-kernel - Re: [PATCH v2 2/2] mm/show_mem: Add trylock while printing alloc info

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Message-ID: <c41c82f0-e5c3-4c2e-b711-3ddf8fcb0135@suse.cz>
Date: Wed, 3 Sep 2025 12:16:45 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: kernel test robot <lkp@...el.com>, Yueyang Pan <pyyjason@...il.com>,
 Suren Baghdasaryan <surenb@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...e.com>,
 Brendan Jackman <jackmanb@...gle.com>, Johannes Weiner <hannes@...xchg.org>,
 Zi Yan <ziy@...dia.com>, Vishal Moola <vishal.moola@...il.com>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Usama Arif <usamaarif642@...il.com>
Cc: oe-kbuild-all@...ts.linux.dev,
 Linux Memory Management List <linux-mm@...ck.org>, kernel-team@...a.com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm/show_mem: Add trylock while printing alloc info

On 9/3/25 11:47, kernel test robot wrote:
> Hi Yueyang,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on akpm-mm/mm-everything]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Yueyang-Pan/mm-show_mem-Dump-the-status-of-the-mem-alloc-profiling-before-printing/20250903-000616
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link:    https://lore.kernel.org/r/1491df0ac12a7626b7c9b00e26a6e10adb8c9045.1756827906.git.pyyjason%40gmail.com
> patch subject: [PATCH v2 2/2] mm/show_mem: Add trylock while printing alloc info
> config: i386-buildonly-randconfig-001-20250903 (https://download.01.org/0day-ci/archive/20250903/202509031744.HcibSETe-lkp@intel.com/config)
> compiler: gcc-13 (Debian 13.3.0-16) 13.3.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250903/202509031744.HcibSETe-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/202509031744.HcibSETe-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from mm/show_mem.c:18:
>    mm/show_mem.c: In function 'show_free_areas':
>    mm/show_mem.c:336:49: error: 'NR_ZSPAGES' undeclared (first use in this function); did you mean 'NR_STATS'?
>      336 |                         K(zone_page_state(zone, NR_ZSPAGES)),
>          |                                                 ^~~~~~~~~~

This is from a different patch and being fixed. Interesting that lkp will
report additional warnings even in presence of prior errors.

>    mm/internal.h:560:16: note: in definition of macro 'K'
>      560 | #define K(x) ((x) << (PAGE_SHIFT-10))
>          |                ^
>    include/linux/printk.h:512:26: note: in expansion of macro 'printk_index_wrap'
>      512 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__)
>          |                          ^~~~~~~~~~~~~~~~~
>    mm/show_mem.c:298:17: note: in expansion of macro 'printk'
>      298 |                 printk(KERN_CONT
>          |                 ^~~~~~
>    mm/show_mem.c:336:49: note: each undeclared identifier is reported only once for each function it appears in
>      336 |                         K(zone_page_state(zone, NR_ZSPAGES)),
>          |                                                 ^~~~~~~~~~
>    mm/internal.h:560:16: note: in definition of macro 'K'
>      560 | #define K(x) ((x) << (PAGE_SHIFT-10))
>          |                ^
>    include/linux/printk.h:512:26: note: in expansion of macro 'printk_index_wrap'
>      512 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__)
>          |                          ^~~~~~~~~~~~~~~~~
>    mm/show_mem.c:298:17: note: in expansion of macro 'printk'
>      298 |                 printk(KERN_CONT
>          |                 ^~~~~~
>    In file included from include/linux/spinlock.h:89,
>                     from include/linux/wait.h:9,
>                     from include/linux/wait_bit.h:8,
>                     from include/linux/fs.h:7,
>                     from include/linux/highmem.h:5,
>                     from include/linux/bvec.h:10,
>                     from include/linux/blk_types.h:10,
>                     from include/linux/blkdev.h:9,
>                     from mm/show_mem.c:8:
>    mm/show_mem.c: In function '__show_mem':
>>> mm/show_mem.c:399:32: warning: unused variable 'mem_alloc_profiling_spinlock' [-Wunused-variable]
>      399 |         static DEFINE_SPINLOCK(mem_alloc_profiling_spinlock);

This is the warning

I think you can simply move the definition to the existing #ifdef
CONFIG_MEM_ALLOC_PROFILING block above the spin_trylock(). The kernel now
uses a new enough C standard to allow this and not only at the beginning of
a cuntion. While not encouraged to do that in general, this seems to be a
valid use case.


>          |                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    include/linux/spinlock_types.h:43:44: note: in definition of macro 'DEFINE_SPINLOCK'
>       43 | #define DEFINE_SPINLOCK(x)      spinlock_t x = __SPIN_LOCK_UNLOCKED(x)
>          |                                            ^
> 
> 
> vim +/mem_alloc_profiling_spinlock +399 mm/show_mem.c
> 
>    396	
>    397	void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
>    398	{
>  > 399		static DEFINE_SPINLOCK(mem_alloc_profiling_spinlock);
>