On Friday, December 02, 2016 10:03:07 AM Qu Wenruo wrote: > [BUG] > For the following case, btrfs can underflow qgroup reserved space > at error path: > (Page size 4K, function name without "btrfs_" prefix) > > Task A | Task B > ---------------------------------------------------------------------- > Buffered_write [0, 2K) | > |- check_data_free_space() | > | |- qgroup_reserve_data() | > | Range aligned to page | > | range [0, 4K) <<< | > | 4K bytes reserved <<< | > |- copy pages to page cache | > | Buffered_write [2K, 4K) > | |- check_data_free_space() > | | |- qgroup_reserved_data() > | | Range alinged to page > | | range [0, 4K) > | | Already reserved by A <<< > | | 0 bytes reserved <<< > | |- delalloc_reserve_metadata() > | | And it *FAILED* (Maybe EQUOTA) > | |- free_reserved_data_space() > |- qgroup_free_data() > Range aligned to page range > [0, 4K) > Freeing 4K > (Special thanks to Chandan for the detailed report and analyse) > > [CAUSE] > Above Task B is freeing reserved data range [0, 4K) which is actually > reserved by Task A. > > And at write back time, page dirty by Task A will go through writeback > routine, which will free 4K reserved data space at file extent insert > time, causing the qgroup underflow. > > [FIX] > For btrfs_qgroup_free_data(), add @reserved parameter to only free > data ranges reserved by previous btrfs_qgroup_reserve_data(). > So in above case, Task B will try to free 0 byte, so no underflow. >
The changes look good to me. Also, I did not notice any regressions when executing fstests with the patch applied. Reviewed-by: Chandan Rajendra <chan...@linux.vnet.ibm.com> Tested-by: Chandan Rajendra <chan...@linux.vnet.ibm.com> -- chandan -- 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
