Hi,
2013-01-18 (금), 16:29 +0300, Dan Carpenter:
> Hello Jaegeuk Kim,
>
> The patch 7bc0900347e0: "f2fs: add garbage collection functions" from
> Nov 2, 2012, has an off-by-one bug.
>
> 429 block_t start_bidx_of_node(unsigned int node_ofs)
> 430 {
> 431 unsigned int indirect_blks = 2 * NIDS_PER_BLOCK + 4;
> 432 unsigned int bidx;
> 433
> 434 if (node_ofs == 0)
> 435 return 0;
> 436
> 437 if (node_ofs <= 2) {
> 438 bidx = node_ofs - 1;
> 439 } else if (node_ofs <= indirect_blks) {
> 440 int dec = (node_ofs - 4) / (NIDS_PER_BLOCK + 1);
>
> If node_ofs == 3 here then (node_ofs - 4) is a very high positive
> number. We divide by 1019 and we get another still very high number but
> not so high that it is negative when cast as an int.If the node_ofs is equal to 3, then it's a run-time bug on its caller, gc_data_segment(), not here itself. In gc_data_segment(), 1. check_dnode(&nofs); 2. start_bidx_of_node(nofs); Here, it means that we don't care about indirect node pages whose node offsets are 3, 3+1018+1, (3+1018+1)+1018+1, and so on. (Ref. *Index Structure* in Document/filesystems/f2fs.txt) Instead, we just check direct node pages only. But, anyway, I'd better write comments to make it clear. Thank you for reviewing. -- Jaegeuk Kim Samsung
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