* [djwong-xfs:vectorized-scrub 260/303] fs/xfs/xfs_reflink.c:169 xfs_reflink_find_shared() warn: variable dereferenced before check 'agbp' (see line 161)
@ 2021-08-17 21:15 kernel test robot
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From: kernel test robot @ 2021-08-17 21:15 UTC (permalink / raw)
To: kbuild
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CC: kbuild-all(a)lists.01.org
CC: "Darrick J. Wong" <darrick.wong@oracle.com>
CC: linux-kernel(a)vger.kernel.org
TO: "Darrick J. Wong" <djwong@kernel.org>
tree: https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git vectorized-scrub
head: 142ad7efefdd71fa40628c868530a9357c18ba27
commit: c41e19cbde3dd4d20aaf146a82f4cb8dfa5944f7 [260/303] xfs: wire up realtime refcount btree cursors
:::::: branch date: 21 hours ago
:::::: commit date: 21 hours ago
config: x86_64-randconfig-m001-20210816 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
New smatch warnings:
fs/xfs/xfs_reflink.c:169 xfs_reflink_find_shared() warn: variable dereferenced before check 'agbp' (see line 161)
Old smatch warnings:
fs/xfs/xfs_reflink.c:651 xfs_reflink_end_cow_extent() warn: missing error code 'error'
vim +/agbp +169 fs/xfs/xfs_reflink.c
3993baeb3c52f4 Darrick J. Wong 2016-10-03 34
3993baeb3c52f4 Darrick J. Wong 2016-10-03 35 /*
3993baeb3c52f4 Darrick J. Wong 2016-10-03 36 * Copy on Write of Shared Blocks
3993baeb3c52f4 Darrick J. Wong 2016-10-03 37 *
3993baeb3c52f4 Darrick J. Wong 2016-10-03 38 * XFS must preserve "the usual" file semantics even when two files share
3993baeb3c52f4 Darrick J. Wong 2016-10-03 39 * the same physical blocks. This means that a write to one file must not
3993baeb3c52f4 Darrick J. Wong 2016-10-03 40 * alter the blocks in a different file; the way that we'll do that is
3993baeb3c52f4 Darrick J. Wong 2016-10-03 41 * through the use of a copy-on-write mechanism. At a high level, that
3993baeb3c52f4 Darrick J. Wong 2016-10-03 42 * means that when we want to write to a shared block, we allocate a new
3993baeb3c52f4 Darrick J. Wong 2016-10-03 43 * block, write the data to the new block, and if that succeeds we map the
3993baeb3c52f4 Darrick J. Wong 2016-10-03 44 * new block into the file.
3993baeb3c52f4 Darrick J. Wong 2016-10-03 45 *
3993baeb3c52f4 Darrick J. Wong 2016-10-03 46 * XFS provides a "delayed allocation" mechanism that defers the allocation
3993baeb3c52f4 Darrick J. Wong 2016-10-03 47 * of disk blocks to dirty-but-not-yet-mapped file blocks as long as
3993baeb3c52f4 Darrick J. Wong 2016-10-03 48 * possible. This reduces fragmentation by enabling the filesystem to ask
3993baeb3c52f4 Darrick J. Wong 2016-10-03 49 * for bigger chunks less often, which is exactly what we want for CoW.
3993baeb3c52f4 Darrick J. Wong 2016-10-03 50 *
3993baeb3c52f4 Darrick J. Wong 2016-10-03 51 * The delalloc mechanism begins when the kernel wants to make a block
3993baeb3c52f4 Darrick J. Wong 2016-10-03 52 * writable (write_begin or page_mkwrite). If the offset is not mapped, we
3993baeb3c52f4 Darrick J. Wong 2016-10-03 53 * create a delalloc mapping, which is a regular in-core extent, but without
3993baeb3c52f4 Darrick J. Wong 2016-10-03 54 * a real startblock. (For delalloc mappings, the startblock encodes both
3993baeb3c52f4 Darrick J. Wong 2016-10-03 55 * a flag that this is a delalloc mapping, and a worst-case estimate of how
3993baeb3c52f4 Darrick J. Wong 2016-10-03 56 * many blocks might be required to put the mapping into the BMBT.) delalloc
3993baeb3c52f4 Darrick J. Wong 2016-10-03 57 * mappings are a reservation against the free space in the filesystem;
3993baeb3c52f4 Darrick J. Wong 2016-10-03 58 * adjacent mappings can also be combined into fewer larger mappings.
3993baeb3c52f4 Darrick J. Wong 2016-10-03 59 *
5eda43000064a6 Darrick J. Wong 2017-02-02 60 * As an optimization, the CoW extent size hint (cowextsz) creates
5eda43000064a6 Darrick J. Wong 2017-02-02 61 * outsized aligned delalloc reservations in the hope of landing out of
5eda43000064a6 Darrick J. Wong 2017-02-02 62 * order nearby CoW writes in a single extent on disk, thereby reducing
5eda43000064a6 Darrick J. Wong 2017-02-02 63 * fragmentation and improving future performance.
5eda43000064a6 Darrick J. Wong 2017-02-02 64 *
5eda43000064a6 Darrick J. Wong 2017-02-02 65 * D: --RRRRRRSSSRRRRRRRR--- (data fork)
5eda43000064a6 Darrick J. Wong 2017-02-02 66 * C: ------DDDDDDD--------- (CoW fork)
5eda43000064a6 Darrick J. Wong 2017-02-02 67 *
3993baeb3c52f4 Darrick J. Wong 2016-10-03 68 * When dirty pages are being written out (typically in writepage), the
5eda43000064a6 Darrick J. Wong 2017-02-02 69 * delalloc reservations are converted into unwritten mappings by
5eda43000064a6 Darrick J. Wong 2017-02-02 70 * allocating blocks and replacing the delalloc mapping with real ones.
5eda43000064a6 Darrick J. Wong 2017-02-02 71 * A delalloc mapping can be replaced by several unwritten ones if the
5eda43000064a6 Darrick J. Wong 2017-02-02 72 * free space is fragmented.
5eda43000064a6 Darrick J. Wong 2017-02-02 73 *
5eda43000064a6 Darrick J. Wong 2017-02-02 74 * D: --RRRRRRSSSRRRRRRRR---
5eda43000064a6 Darrick J. Wong 2017-02-02 75 * C: ------UUUUUUU---------
3993baeb3c52f4 Darrick J. Wong 2016-10-03 76 *
3993baeb3c52f4 Darrick J. Wong 2016-10-03 77 * We want to adapt the delalloc mechanism for copy-on-write, since the
3993baeb3c52f4 Darrick J. Wong 2016-10-03 78 * write paths are similar. The first two steps (creating the reservation
3993baeb3c52f4 Darrick J. Wong 2016-10-03 79 * and allocating the blocks) are exactly the same as delalloc except that
3993baeb3c52f4 Darrick J. Wong 2016-10-03 80 * the mappings must be stored in a separate CoW fork because we do not want
3993baeb3c52f4 Darrick J. Wong 2016-10-03 81 * to disturb the mapping in the data fork until we're sure that the write
3993baeb3c52f4 Darrick J. Wong 2016-10-03 82 * succeeded. IO completion in this case is the process of removing the old
3993baeb3c52f4 Darrick J. Wong 2016-10-03 83 * mapping from the data fork and moving the new mapping from the CoW fork to
3993baeb3c52f4 Darrick J. Wong 2016-10-03 84 * the data fork. This will be discussed shortly.
3993baeb3c52f4 Darrick J. Wong 2016-10-03 85 *
3993baeb3c52f4 Darrick J. Wong 2016-10-03 86 * For now, unaligned directio writes will be bounced back to the page cache.
3993baeb3c52f4 Darrick J. Wong 2016-10-03 87 * Block-aligned directio writes will use the same mechanism as buffered
3993baeb3c52f4 Darrick J. Wong 2016-10-03 88 * writes.
3993baeb3c52f4 Darrick J. Wong 2016-10-03 89 *
5eda43000064a6 Darrick J. Wong 2017-02-02 90 * Just prior to submitting the actual disk write requests, we convert
5eda43000064a6 Darrick J. Wong 2017-02-02 91 * the extents representing the range of the file actually being written
5eda43000064a6 Darrick J. Wong 2017-02-02 92 * (as opposed to extra pieces created for the cowextsize hint) to real
5eda43000064a6 Darrick J. Wong 2017-02-02 93 * extents. This will become important in the next step:
5eda43000064a6 Darrick J. Wong 2017-02-02 94 *
5eda43000064a6 Darrick J. Wong 2017-02-02 95 * D: --RRRRRRSSSRRRRRRRR---
5eda43000064a6 Darrick J. Wong 2017-02-02 96 * C: ------UUrrUUU---------
5eda43000064a6 Darrick J. Wong 2017-02-02 97 *
3993baeb3c52f4 Darrick J. Wong 2016-10-03 98 * CoW remapping must be done after the data block write completes,
3993baeb3c52f4 Darrick J. Wong 2016-10-03 99 * because we don't want to destroy the old data fork map until we're sure
3993baeb3c52f4 Darrick J. Wong 2016-10-03 100 * the new block has been written. Since the new mappings are kept in a
3993baeb3c52f4 Darrick J. Wong 2016-10-03 101 * separate fork, we can simply iterate these mappings to find the ones
3993baeb3c52f4 Darrick J. Wong 2016-10-03 102 * that cover the file blocks that we just CoW'd. For each extent, simply
3993baeb3c52f4 Darrick J. Wong 2016-10-03 103 * unmap the corresponding range in the data fork, map the new range into
5eda43000064a6 Darrick J. Wong 2017-02-02 104 * the data fork, and remove the extent from the CoW fork. Because of
5eda43000064a6 Darrick J. Wong 2017-02-02 105 * the presence of the cowextsize hint, however, we must be careful
5eda43000064a6 Darrick J. Wong 2017-02-02 106 * only to remap the blocks that we've actually written out -- we must
5eda43000064a6 Darrick J. Wong 2017-02-02 107 * never remap delalloc reservations nor CoW staging blocks that have
5eda43000064a6 Darrick J. Wong 2017-02-02 108 * yet to be written. This corresponds exactly to the real extents in
5eda43000064a6 Darrick J. Wong 2017-02-02 109 * the CoW fork:
5eda43000064a6 Darrick J. Wong 2017-02-02 110 *
5eda43000064a6 Darrick J. Wong 2017-02-02 111 * D: --RRRRRRrrSRRRRRRRR---
5eda43000064a6 Darrick J. Wong 2017-02-02 112 * C: ------UU--UUU---------
3993baeb3c52f4 Darrick J. Wong 2016-10-03 113 *
3993baeb3c52f4 Darrick J. Wong 2016-10-03 114 * Since the remapping operation can be applied to an arbitrary file
3993baeb3c52f4 Darrick J. Wong 2016-10-03 115 * range, we record the need for the remap step as a flag in the ioend
3993baeb3c52f4 Darrick J. Wong 2016-10-03 116 * instead of declaring a new IO type. This is required for direct io
3993baeb3c52f4 Darrick J. Wong 2016-10-03 117 * because we only have ioend for the whole dio, and we have to be able to
3993baeb3c52f4 Darrick J. Wong 2016-10-03 118 * remember the presence of unwritten blocks and CoW blocks with a single
3993baeb3c52f4 Darrick J. Wong 2016-10-03 119 * ioend structure. Better yet, the more ground we can cover with one
3993baeb3c52f4 Darrick J. Wong 2016-10-03 120 * ioend, the better.
3993baeb3c52f4 Darrick J. Wong 2016-10-03 121 */
2a06705cd59540 Darrick J. Wong 2016-10-03 122
2a06705cd59540 Darrick J. Wong 2016-10-03 123 /*
2a916659ca4d4a Darrick J. Wong 2021-01-05 124 * Given an AG extent, find the lowest-numbered run of shared blocks within
2a916659ca4d4a Darrick J. Wong 2021-01-05 125 * that range and return the range in fbno/flen. If find_end_of_shared is
2a916659ca4d4a Darrick J. Wong 2021-01-05 126 * true, return the longest contiguous extent of shared blocks. If there are
2a916659ca4d4a Darrick J. Wong 2021-01-05 127 * no shared extents, fbno and flen will be set to NULLFSBLOCK and 0,
2a916659ca4d4a Darrick J. Wong 2021-01-05 128 * respectively.
2a06705cd59540 Darrick J. Wong 2016-10-03 129 */
2a916659ca4d4a Darrick J. Wong 2021-01-05 130 STATIC int
2a06705cd59540 Darrick J. Wong 2016-10-03 131 xfs_reflink_find_shared(
2a916659ca4d4a Darrick J. Wong 2021-01-05 132 struct xfs_inode *ip,
92ff7285f1df55 Darrick J. Wong 2017-06-16 133 struct xfs_trans *tp,
2a916659ca4d4a Darrick J. Wong 2021-01-05 134 struct xfs_bmbt_irec *irec,
2a916659ca4d4a Darrick J. Wong 2021-01-05 135 xfs_fsblock_t *fbno,
2a916659ca4d4a Darrick J. Wong 2021-01-05 136 xfs_filblks_t *flen,
2a06705cd59540 Darrick J. Wong 2016-10-03 137 bool find_end_of_shared)
2a06705cd59540 Darrick J. Wong 2016-10-03 138 {
2a916659ca4d4a Darrick J. Wong 2021-01-05 139 struct xfs_mount *mp = ip->i_mount;
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 140 struct xfs_buf *agbp = NULL;
2a06705cd59540 Darrick J. Wong 2016-10-03 141 struct xfs_btree_cur *cur;
2a916659ca4d4a Darrick J. Wong 2021-01-05 142 xfs_agnumber_t agno;
a42a3ab16973ba Darrick J. Wong 2021-01-05 143 xfs_fsblock_t agbno;
a42a3ab16973ba Darrick J. Wong 2021-01-05 144 xfs_fsblock_t shared_bno;
a42a3ab16973ba Darrick J. Wong 2021-01-05 145 xfs_filblks_t shared_len;
2a06705cd59540 Darrick J. Wong 2016-10-03 146 int error;
2a06705cd59540 Darrick J. Wong 2016-10-03 147
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 148 if (XFS_IS_REALTIME_INODE(ip)) {
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 149 agno = NULLAGNUMBER;
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 150 agbno = irec->br_startblock;
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 151 xfs_rtlock(NULL, mp, XFS_RTLOCK_REFCOUNT);
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 152 cur = xfs_rtrefcountbt_init_cursor(mp, tp, mp->m_rrefcountip);
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 153 } else {
2a916659ca4d4a Darrick J. Wong 2021-01-05 154 agno = XFS_FSB_TO_AGNO(mp, irec->br_startblock);
2a916659ca4d4a Darrick J. Wong 2021-01-05 155 agbno = XFS_FSB_TO_AGBNO(mp, irec->br_startblock);
2a916659ca4d4a Darrick J. Wong 2021-01-05 156
92ff7285f1df55 Darrick J. Wong 2017-06-16 157 error = xfs_alloc_read_agf(mp, tp, agno, 0, &agbp);
2a06705cd59540 Darrick J. Wong 2016-10-03 158 if (error)
2a06705cd59540 Darrick J. Wong 2016-10-03 159 return error;
2a06705cd59540 Darrick J. Wong 2016-10-03 160
a81a06211fb43d Dave Chinner 2021-06-02 @161 cur = xfs_refcountbt_init_cursor(mp, tp, agbp, agbp->b_pag);
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 162 }
2a06705cd59540 Darrick J. Wong 2016-10-03 163
2a916659ca4d4a Darrick J. Wong 2021-01-05 164 error = xfs_refcount_find_shared(cur, agbno, irec->br_blockcount,
2a916659ca4d4a Darrick J. Wong 2021-01-05 165 &shared_bno, &shared_len, find_end_of_shared);
2a06705cd59540 Darrick J. Wong 2016-10-03 166
0b04b6b875b32f Darrick J. Wong 2018-07-19 167 xfs_btree_del_cursor(cur, error);
2a06705cd59540 Darrick J. Wong 2016-10-03 168
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 @169 if (agbp)
92ff7285f1df55 Darrick J. Wong 2017-06-16 170 xfs_trans_brelse(tp, agbp);
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 171 else
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 172 xfs_rtunlock(mp, XFS_RTLOCK_REFCOUNT);
2a916659ca4d4a Darrick J. Wong 2021-01-05 173
a42a3ab16973ba Darrick J. Wong 2021-01-05 174 if (shared_bno == NULLFSBLOCK)
2a916659ca4d4a Darrick J. Wong 2021-01-05 175 *fbno = NULLFSBLOCK;
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 176 else if (XFS_IS_REALTIME_INODE(ip))
c41e19cbde3dd4 Darrick J. Wong 2021-01-05 177 *fbno = shared_bno;
2a916659ca4d4a Darrick J. Wong 2021-01-05 178 else
2a916659ca4d4a Darrick J. Wong 2021-01-05 179 *fbno = XFS_AGB_TO_FSB(mp, agno, shared_bno);
2a916659ca4d4a Darrick J. Wong 2021-01-05 180 *flen = shared_len;
2a06705cd59540 Darrick J. Wong 2016-10-03 181 return error;
2a06705cd59540 Darrick J. Wong 2016-10-03 182 }
2a06705cd59540 Darrick J. Wong 2016-10-03 183
---
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2021-08-17 21:15 [djwong-xfs:vectorized-scrub 260/303] fs/xfs/xfs_reflink.c:169 xfs_reflink_find_shared() warn: variable dereferenced before check 'agbp' (see line 161) kernel test robot
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