Re: [RFC 2/4] buffer: add alloc_folio_buffers() helper

[kernel test robot <lkp@intel.com>]

Hi Pankaj,

[This is a private test report for your RFC patch.]
kernel test robot noticed the following build warnings:

[auto build test WARNING on vfs-idmapping/for-next]
[also build test WARNING on linus/master v6.3-rc6 next-20230413]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Pankaj-Raghav/buffer-add-alloc_folio_buffers-helper/20230414-200852
base:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/idmapping.git for-next
patch link:    https://lore.kernel.org/r/20230414110821.21548-3-p.raghav%40samsung.com
patch subject: [RFC 2/4] buffer: add alloc_folio_buffers() helper
config: riscv-allnoconfig (https://download.01.org/0day-ci/archive/20230414/202304142125.IA2eKPjg-lkp@intel.com/config)
compiler: riscv64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/a5c44e7a616f7a972e4570437b81778c20c15137
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Pankaj-Raghav/buffer-add-alloc_folio_buffers-helper/20230414-200852
        git checkout a5c44e7a616f7a972e4570437b81778c20c15137
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304142125.IA2eKPjg-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> fs/buffer.c:913:21: warning: no previous prototype for 'alloc_folio_buffers' [-Wmissing-prototypes]
     913 | struct buffer_head *alloc_folio_buffers(struct folio *folio, unsigned long size,
         |                     ^~~~~~~~~~~~~~~~~~~


vim +/alloc_folio_buffers +913 fs/buffer.c

   903	
   904	/*
   905	 * Create the appropriate buffers when given a folio for data area and
   906	 * the size of each buffer.. Use the bh->b_this_page linked list to
   907	 * follow the buffers created.  Return NULL if unable to create more
   908	 * buffers.
   909	 *
   910	 * The retry flag is used to differentiate async IO (paging, swapping)
   911	 * which may not fail from ordinary buffer allocations.
   912	 */
 > 913	struct buffer_head *alloc_folio_buffers(struct folio *folio, unsigned long size,
   914						bool retry)
   915	{
   916		struct buffer_head *bh, *head;
   917		gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
   918		long offset;
   919		struct mem_cgroup *memcg, *old_memcg;
   920	
   921		if (retry)
   922			gfp |= __GFP_NOFAIL;
   923	
   924		/* The folio lock pins the memcg */
   925		memcg = folio_memcg(folio);
   926		old_memcg = set_active_memcg(memcg);
   927	
   928		head = NULL;
   929		offset = folio_size(folio);
   930		while ((offset -= size) >= 0) {
   931			bh = alloc_buffer_head(gfp);
   932			if (!bh)
   933				goto no_grow;
   934	
   935			bh->b_this_page = head;
   936			bh->b_blocknr = -1;
   937			head = bh;
   938	
   939			bh->b_size = size;
   940	
   941			/* Link the buffer to its folio */
   942			set_bh_folio(bh, folio, offset);
   943		}
   944	out:
   945		set_active_memcg(old_memcg);
   946		return head;
   947	/*
   948	 * In case anything failed, we just free everything we got.
   949	 */
   950	no_grow:
   951		if (head) {
   952			do {
   953				bh = head;
   954				head = head->b_this_page;
   955				free_buffer_head(bh);
   956			} while (head);
   957		}
   958	
   959		goto out;
   960	}
   961	EXPORT_SYMBOL_GPL(alloc_folio_buffers);
   962	

-- 
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https://github.com/intel/lkp-tests