[dhowells-fs:netfs-writeback 17/22] fs/netfs/write_collect.c:110 netfs_writeback_lookup_folio() error: we previously assumed 'folio' could be null (see line 99)

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

BCC: lkp@intel.com
CC: oe-kbuild-all@lists.linux.dev
TO: David Howells <dhowells@redhat.com>

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git netfs-writeback
head:   6d4dafd8301ee8645d4814a7e75a9135acf67613
commit: 52ff5a10870495fafb8bdf0ee2e987d861b1b42c [17/22] netfs, 9p: Implement helpers for new write code
:::::: branch date: 2 days ago
:::::: commit date: 2 days ago
config: sparc64-randconfig-r081-20240323 (https://download.01.org/0day-ci/archive/20240323/202403232142.egfToXYX-lkp@intel.com/config)
compiler: sparc64-linux-gcc (GCC) 13.2.0

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
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <error27@gmail.com>
| Closes: https://lore.kernel.org/r/202403232142.egfToXYX-lkp@intel.com/

smatch warnings:
fs/netfs/write_collect.c:110 netfs_writeback_lookup_folio() error: we previously assumed 'folio' could be null (see line 99)

vim +/folio +110 fs/netfs/write_collect.c

9a3702e1d161f5 David Howells 2024-03-18   81  
9a3702e1d161f5 David Howells 2024-03-18   82  /*
9a3702e1d161f5 David Howells 2024-03-18   83   * Get hold of a folio we have under writeback.  We don't want to get the
9a3702e1d161f5 David Howells 2024-03-18   84   * refcount on it.
9a3702e1d161f5 David Howells 2024-03-18   85   */
9a3702e1d161f5 David Howells 2024-03-18   86  static struct folio *netfs_writeback_lookup_folio(struct netfs_io_request *wreq, loff_t pos)
9a3702e1d161f5 David Howells 2024-03-18   87  {
9a3702e1d161f5 David Howells 2024-03-18   88  	XA_STATE(xas, &wreq->mapping->i_pages, pos / PAGE_SIZE);
9a3702e1d161f5 David Howells 2024-03-18   89  	struct folio *folio;
9a3702e1d161f5 David Howells 2024-03-18   90  
9a3702e1d161f5 David Howells 2024-03-18   91  	rcu_read_lock();
9a3702e1d161f5 David Howells 2024-03-18   92  
9a3702e1d161f5 David Howells 2024-03-18   93  	for (;;) {
9a3702e1d161f5 David Howells 2024-03-18   94  		xas_reset(&xas);
9a3702e1d161f5 David Howells 2024-03-18   95  		folio = xas_load(&xas);
9a3702e1d161f5 David Howells 2024-03-18   96  		if (xas_retry(&xas, folio))
9a3702e1d161f5 David Howells 2024-03-18   97  			continue;
9a3702e1d161f5 David Howells 2024-03-18   98  
9a3702e1d161f5 David Howells 2024-03-18  @99  		if (!folio || xa_is_value(folio))
9a3702e1d161f5 David Howells 2024-03-18  100  			kdebug("R=%08x: folio %lx (%llx) not present",
9a3702e1d161f5 David Howells 2024-03-18  101  			       wreq->debug_id, xas.xa_index, pos / PAGE_SIZE);
9a3702e1d161f5 David Howells 2024-03-18  102  		BUG_ON(!folio || xa_is_value(folio));
9a3702e1d161f5 David Howells 2024-03-18  103  
9a3702e1d161f5 David Howells 2024-03-18  104  		if (folio == xas_reload(&xas))
9a3702e1d161f5 David Howells 2024-03-18  105  			break;
9a3702e1d161f5 David Howells 2024-03-18  106  	}
9a3702e1d161f5 David Howells 2024-03-18  107  
9a3702e1d161f5 David Howells 2024-03-18  108  	rcu_read_unlock();
9a3702e1d161f5 David Howells 2024-03-18  109  
9a3702e1d161f5 David Howells 2024-03-18 @110  	if (WARN_ONCE(!folio_test_writeback(folio),
9a3702e1d161f5 David Howells 2024-03-18  111  		      "R=%08x: folio %lx is not under writeback\n",
9a3702e1d161f5 David Howells 2024-03-18  112  		      wreq->debug_id, folio->index)) {
9a3702e1d161f5 David Howells 2024-03-18  113  		trace_netfs_folio(folio, netfs_folio_trace_not_under_wback);
9a3702e1d161f5 David Howells 2024-03-18  114  	}
9a3702e1d161f5 David Howells 2024-03-18  115  	return folio;
9a3702e1d161f5 David Howells 2024-03-18  116  }
9a3702e1d161f5 David Howells 2024-03-18  117  

:::::: The code at line 110 was first introduced by commit
:::::: 9a3702e1d161f5b03a7b42122f9f693af1144fc8 netfs: New writeback implementation

:::::: TO: David Howells <dhowells@redhat.com>
:::::: CC: David Howells <dhowells@redhat.com>

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