Re: [PATCH 2/7] vfs: add inode iteration superblock method

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

Hi Dave,

kernel test robot noticed the following build warnings:

[auto build test WARNING on brauner-vfs/vfs.all]
[also build test WARNING on xfs-linux/for-next axboe-block/for-next linus/master v6.12-rc1 next-20241004]
[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/Dave-Chinner/vfs-replace-invalidate_inodes-with-evict_inodes/20241002-094254
base:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git vfs.all
patch link:    https://lore.kernel.org/r/20241002014017.3801899-3-david%40fromorbit.com
patch subject: [PATCH 2/7] vfs: add inode iteration superblock method
config: openrisc-allnoconfig (https://download.01.org/0day-ci/archive/20241004/202410041724.REiCiIEQ-lkp@intel.com/config)
compiler: or1k-linux-gcc (GCC) 14.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241004/202410041724.REiCiIEQ-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202410041724.REiCiIEQ-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> fs/super.c:183: warning: Function parameter or struct member 'private_data' not described in 'super_iter_inodes'
>> fs/super.c:183: warning: Function parameter or struct member 'flags' not described in 'super_iter_inodes'
>> fs/super.c:241: warning: bad line: 
>> fs/super.c:260: warning: Function parameter or struct member 'private_data' not described in 'super_iter_inodes_unsafe'


vim +183 fs/super.c

   169	
   170	/**
   171	 * super_iter_inodes - iterate all the cached inodes on a superblock
   172	 * @sb: superblock to iterate
   173	 * @iter_fn: callback to run on every inode found.
   174	 *
   175	 * This function iterates all cached inodes on a superblock that are not in
   176	 * the process of being initialised or torn down. It will run @iter_fn() with
   177	 * a valid, referenced inode, so it is safe for the caller to do anything
   178	 * it wants with the inode except drop the reference the iterator holds.
   179	 *
   180	 */
   181	int super_iter_inodes(struct super_block *sb, ino_iter_fn iter_fn,
   182			void *private_data, int flags)
 > 183	{
   184		struct inode *inode, *old_inode = NULL;
   185		int ret = 0;
   186	
   187		spin_lock(&sb->s_inode_list_lock);
   188		list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
   189			spin_lock(&inode->i_lock);
   190			if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
   191				spin_unlock(&inode->i_lock);
   192				continue;
   193			}
   194	
   195			/*
   196			 * Skip over zero refcount inode if the caller only wants
   197			 * referenced inodes to be iterated.
   198			 */
   199			if ((flags & INO_ITER_REFERENCED) &&
   200			    !atomic_read(&inode->i_count)) {
   201				spin_unlock(&inode->i_lock);
   202				continue;
   203			}
   204	
   205			__iget(inode);
   206			spin_unlock(&inode->i_lock);
   207			spin_unlock(&sb->s_inode_list_lock);
   208			iput(old_inode);
   209	
   210			ret = iter_fn(inode, private_data);
   211	
   212			old_inode = inode;
   213			if (ret == INO_ITER_ABORT) {
   214				ret = 0;
   215				break;
   216			}
   217			if (ret < 0)
   218				break;
   219	
   220			cond_resched();
   221			spin_lock(&sb->s_inode_list_lock);
   222		}
   223		spin_unlock(&sb->s_inode_list_lock);
   224		iput(old_inode);
   225		return ret;
   226	}
   227	
   228	/**
   229	 * super_iter_inodes_unsafe - unsafely iterate all the inodes on a superblock
   230	 * @sb: superblock to iterate
   231	 * @iter_fn: callback to run on every inode found.
   232	 *
   233	 * This is almost certainly not the function you want. It is for internal VFS
   234	 * operations only. Please use super_iter_inodes() instead. If you must use
   235	 * this function, please add a comment explaining why it is necessary and the
   236	 * locking that makes it safe to use this function.
   237	 *
   238	 * This function iterates all cached inodes on a superblock that are attached to
   239	 * the superblock. It will pass each inode to @iter_fn unlocked and without
   240	 * having performed any existences checks on it.
 > 241	
   242	 * @iter_fn must perform all necessary state checks on the inode itself to
   243	 * ensure safe operation. super_iter_inodes_unsafe() only guarantees that the
   244	 * inode exists and won't be freed whilst the callback is running.
   245	 *
   246	 * @iter_fn must not block. It is run in an atomic context that is not allowed
   247	 * to sleep to provide the inode existence guarantees. If the callback needs to
   248	 * do blocking operations it needs to track the inode itself and defer those
   249	 * operations until after the iteration completes.
   250	 *
   251	 * @iter_fn must provide conditional reschedule checks itself. If rescheduling
   252	 * or deferred processing is needed, it must return INO_ITER_ABORT to return to
   253	 * the high level function to perform those operations. It can then restart the
   254	 * iteration again. The high level code must provide forwards progress
   255	 * guarantees if they are necessary.
   256	 *
   257	 */
   258	void super_iter_inodes_unsafe(struct super_block *sb, ino_iter_fn iter_fn,
   259			void *private_data)
 > 260	{
   261		struct inode *inode;
   262		int ret;
   263	
   264		rcu_read_lock();
   265		spin_lock(&sb->s_inode_list_lock);
   266		list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
   267			ret = iter_fn(inode, private_data);
   268			if (ret == INO_ITER_ABORT)
   269				break;
   270		}
   271		spin_unlock(&sb->s_inode_list_lock);
   272		rcu_read_unlock();
   273	}
   274	

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