On 2018年05月09日 21:00, David Sterba wrote: > On Fri, May 04, 2018 at 01:56:59PM +0800, Qu Wenruo wrote: >> Under the following case, qgroup rescan can double account cowed tree >> blocks: >> >> In this case, extent tree only has one tree block. >> >> - >> | transid=5 last committed=4 >> | btrfs_qgroup_rescan_worker() >> | |- btrfs_start_transaction() >> | | transid = 5 >> | |- qgroup_rescan_leaf() >> | |- btrfs_search_slot_for_read() on extent tree >> | Get the only extent tree block from commit root (transid = 4). >> | Scan it, set qgroup_rescan_progress to the last >> | EXTENT/META_ITEM + 1 >> | now qgroup_rescan_progress = A + 1. >> | >> | fs tree get CoWed, new tree block is at A + 16K >> | transid 5 get committed >> - >> | transid=6 last committed=5 >> | btrfs_qgroup_rescan_worker() >> | btrfs_qgroup_rescan_worker() >> | |- btrfs_start_transaction() >> | | transid = 5 >> | |- qgroup_rescan_leaf() >> | |- btrfs_search_slot_for_read() on extent tree >> | Get the only extent tree block from commit root (transid = 5). >> | scan it using qgroup_rescan_progress (A + 1). >> | found new tree block beyong A, and it's fs tree block, >> | account it to increase qgroup numbers. >> - >> >> In above case, tree block A, and tree block A + 16K get accounted twice, >> while qgroup rescan should stop when it already reach the last leaf, >> other than continue using its qgroup_rescan_progress. >> >> Such case could happen by just looping btrfs/017 and with some >> possibility it can hit such double qgroup accounting problem. >> >> Fix it by checking the path to determine if we should finish qgroup >> rescan, other than relying on next loop to exit. >> >> Reported-by: Nikolay Borisov <nbori...@suse.com> >> Signed-off-by: Qu Wenruo <w...@suse.com> > > Is this something for 4.17-rc ?
No need to hurry. It would be OK for next release since it's not some regression, but a long existing bug. Thanks, Qu > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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