[dhowells-fs:netfs-next 24/24] fs/netfs/write_collect.c:155:7: warning: variable 'fpos' is used uninitialized whenever 'if' condition is true

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

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git netfs-next
head:   4b31f42776fcd3c9eaf2c27084026e98aeed5ddc
commit: 4b31f42776fcd3c9eaf2c27084026e98aeed5ddc [24/24] netfs: Combine prepare and issue ops and grab the buffers on request
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20260717/202607172354.5AwTxoqH-lkp@intel.com/config)
compiler: clang version 22.1.8 (https://github.com/llvm/llvm-project ca7933e47d3a3451d81e72ac174dcb5aa28b59d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260717/202607172354.5AwTxoqH-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/202607172354.5AwTxoqH-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> fs/netfs/write_collect.c:155:7: warning: variable 'fpos' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
     155 |                 if (!bvecq->bv[slot].bv_page) {
         |                     ^~~~~~~~~~~~~~~~~~~~~~~~
   fs/netfs/write_collect.c:187:7: note: uninitialized use occurs here
     187 |                 if (fpos + fsize >= collected_to)
         |                     ^~~~
   fs/netfs/write_collect.c:155:3: note: remove the 'if' if its condition is always false
     155 |                 if (!bvecq->bv[slot].bv_page) {
         |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     156 |                         WARN_ONCE(1, "R=%08x slot already cleared?\n", wreq->debug_id);
         |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     157 |                         fsize = bvecq->bv[slot].bv_len;
         |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     158 |                         goto skip;
         |                         ~~~~~~~~~~
     159 |                 }
         |                 ~
   fs/netfs/write_collect.c:137:26: note: initialize the variable 'fpos' to silence this warning
     137 |                 unsigned long long fpos, fend;
         |                                        ^
         |                                         = 0
   1 warning generated.


vim +155 fs/netfs/write_collect.c

   111	
   112	/*
   113	 * Unlock any folios we've finished with.
   114	 */
   115	static void netfs_writeback_unlock_folios(struct netfs_io_request *wreq,
   116						  unsigned int *notes)
   117	{
   118		struct bvecq *bvecq = wreq->collect_cursor.bvecq;
   119		unsigned long long collected_to = wreq->collected_to;
   120		unsigned int slot = wreq->collect_cursor.slot;
   121	
   122		if (WARN_ON_ONCE(!bvecq)) {
   123			pr_err("[!] Writeback unlock found empty buffer!\n");
   124			netfs_dump_request(wreq);
   125			return;
   126		}
   127	
   128		if (wreq->origin == NETFS_PGPRIV2_COPY_TO_CACHE) {
   129			if (netfs_pgpriv2_unlock_copied_folios(wreq))
   130				*notes |= MADE_PROGRESS;
   131			return;
   132		}
   133	
   134		for (;;) {
   135			struct folio *folio;
   136			struct netfs_folio *finfo;
   137			unsigned long long fpos, fend;
   138			size_t fsize, flen;
   139	
   140			/* Try to clean up the head of the queue if it appears to be
   141			 * used up, but we need to be very careful - the cleanup can
   142			 * catch the dispatcher, which could lead to us having nothing
   143			 * left in the queue, causing the front and back pointers to
   144			 * end up on different tracks.  To avoid this, we must always
   145			 * keep at least one segment in the queue.
   146			 */
   147			if (!bvecq_acquire_slot(bvecq, slot)) {
   148				wreq->collect_cursor.slot = slot;
   149				if (!bvecq_delete_spent(&wreq->collect_cursor))
   150					return;
   151				bvecq = wreq->collect_cursor.bvecq;
   152				slot  = wreq->collect_cursor.slot;
   153			}
   154	
 > 155			if (!bvecq->bv[slot].bv_page) {
   156				WARN_ONCE(1, "R=%08x slot already cleared?\n", wreq->debug_id);
   157				fsize = bvecq->bv[slot].bv_len;
   158				goto skip;
   159			}
   160	
   161			folio = page_folio(bvecq->bv[slot].bv_page);
   162			if (WARN_ONCE(!folio_test_writeback(folio),
   163				      "R=%08x: folio %lx is not under writeback\n",
   164				      wreq->debug_id, folio->index))
   165				trace_netfs_folio(folio, netfs_folio_trace_not_under_wback);
   166	
   167			fpos = folio_pos(folio);
   168			fsize = folio_size(folio);
   169			finfo = netfs_folio_info(folio);
   170			flen = finfo ? finfo->dirty_offset + finfo->dirty_len : fsize;
   171	
   172			fend = min_t(unsigned long long, fpos + flen, wreq->i_size);
   173	
   174			trace_netfs_collect_folio(wreq, folio, fend, collected_to);
   175	
   176			/* Unlock any folio we've transferred all of. */
   177			if (collected_to < fend)
   178				break;
   179	
   180			wreq->nr_group_rel += netfs_folio_written_back(folio);
   181			wreq->cleaned_to = fpos + fsize;
   182			*notes |= MADE_PROGRESS;
   183	
   184			bvecq->bv[slot].bv_page = NULL;
   185		skip:
   186			slot++;
   187			if (fpos + fsize >= collected_to)
   188				break;
   189		}
   190	
   191		wreq->collect_cursor.slot = slot;
   192	}
   193	

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