[bug report] xfs: allow setting and clearing of log incompat feature flags

[Dan Carpenter <error27@gmail.com>]

Hello Darrick J. Wong,

The patch 908ce71e54f8: "xfs: allow setting and clearing of log
incompat feature flags" from Aug 8, 2021, leads to the following
Smatch static checker warning:

	fs/xfs/xfs_mount.c:1315 xfs_add_incompat_log_feature()
	warn: missing error code 'error'

fs/xfs/xfs_mount.c
    1280 int
    1281 xfs_add_incompat_log_feature(
    1282         struct xfs_mount        *mp,
    1283         uint32_t                feature)
    1284 {
    1285         struct xfs_dsb                *dsb;
    1286         int                        error;
    1287 
    1288         ASSERT(hweight32(feature) == 1);
    1289         ASSERT(!(feature & XFS_SB_FEAT_INCOMPAT_LOG_UNKNOWN));
    1290 
    1291         /*
    1292          * Force the log to disk and kick the background AIL thread to reduce
    1293          * the chances that the bwrite will stall waiting for the AIL to unpin
    1294          * the primary superblock buffer.  This isn't a data integrity
    1295          * operation, so we don't need a synchronous push.
    1296          */
    1297         error = xfs_log_force(mp, XFS_LOG_SYNC);
    1298         if (error)
    1299                 return error;
    1300         xfs_ail_push_all(mp->m_ail);
    1301 
    1302         /*
    1303          * Lock the primary superblock buffer to serialize all callers that
    1304          * are trying to set feature bits.
    1305          */
    1306         xfs_buf_lock(mp->m_sb_bp);
    1307         xfs_buf_hold(mp->m_sb_bp);
    1308 
    1309         if (xfs_is_shutdown(mp)) {
    1310                 error = -EIO;
    1311                 goto rele;
    1312         }
    1313 
    1314         if (xfs_sb_has_incompat_log_feature(&mp->m_sb, feature))
--> 1315                 goto rele;
                         ^^^^^^^^^
It's not clear to me, why this old code is suddenly showing up as a new
warning...  But it does feel like it should be an error path.

    1316 
    1317         /*
    1318          * Write the primary superblock to disk immediately, because we need
    1319          * the log_incompat bit to be set in the primary super now to protect
    1320          * the log items that we're going to commit later.
    1321          */
    1322         dsb = mp->m_sb_bp->b_addr;
    1323         xfs_sb_to_disk(dsb, &mp->m_sb);
    1324         dsb->sb_features_log_incompat |= cpu_to_be32(feature);
    1325         error = xfs_bwrite(mp->m_sb_bp);
    1326         if (error)
    1327                 goto shutdown;
    1328 
    1329         /*
    1330          * Add the feature bits to the incore superblock before we unlock the
    1331          * buffer.
    1332          */
    1333         xfs_sb_add_incompat_log_features(&mp->m_sb, feature);
    1334         xfs_buf_relse(mp->m_sb_bp);
    1335 
    1336         /* Log the superblock to disk. */
    1337         return xfs_sync_sb(mp, false);
    1338 shutdown:
    1339         xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
    1340 rele:
    1341         xfs_buf_relse(mp->m_sb_bp);
    1342         return error;
    1343 }

regards,
dan carpenter