Re: [linux-next:master] BUILD REGRESSION 605cbf3d5f20470ec303b79feda3202935f4a142

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 21 Aug 2020 04:26:12 +0800 kernel test robot <lkp@intel.com> wrote:

> tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  master
> branch HEAD: 605cbf3d5f20470ec303b79feda3202935f4a142  Add linux-next specific files for 20200820
> 
> Error/Warning in current branch:
> 
> fs/notify/fsnotify.c:460 fsnotify() warn: variable dereferenced before check 'inode' (see line 449)

Yes, this:

:	if (!inode) {
: 		/* Dirent event - report on TYPE_INODE to dir */
: 		inode = dir;
: 	} else if (mask & FS_EVENT_ON_CHILD) {
: 		/*
: 		 * Event on child - report on TYPE_INODE to dir if it is
: 		 * watching children and on TYPE_CHILD to child.
: 		 */
: 		child = inode;
: 		inode = dir;
: 	}

`inode' is non-NULL here.

: 	sb = inode->i_sb;

So this is OK.

: 	/*
: 	 * Optimization: srcu_read_lock() has a memory barrier which can
: 	 * be expensive.  It protects walking the *_fsnotify_marks lists.
: 	 * However, if we do not walk the lists, we do not have to do
: 	 * SRCU because we have no references to any objects and do not
: 	 * need SRCU to keep them "alive".
: 	 */
: 	if (!sb->s_fsnotify_marks &&
: 	    (!mnt || !mnt->mnt_fsnotify_marks) &&
: 	    (!inode || !inode->i_fsnotify_marks) &&

So !inode is always false.

: 	    (!child || !child->i_fsnotify_marks))
: 		return 0;

I assume we can just zap the "!inode ||".  Amir & Jan, can you
please take a look?