Btrfs: fix panic when starting bg cache writeout after IO error
When waiting for the writeback of block group cache we returned immediately if there was an error during writeback without waiting for the ordered extent to complete. This left a short time window where if some other task attempts to start the writeout for the same block group cache it can attempt to add a new ordered extent, starting at the same offset (0) before the previous one is removed from the ordered tree, causing an ordered tree panic (calls BUG()). This normally doesn't happen in other write paths, such as buffered writes or direct IO writes for regular files, since before marking page ranges dirty we lock the ranges and wait for any ordered extents within the range to complete first. Fix this by making btrfs_wait_ordered_range() not return immediately if it gets an error from the writeback, waiting for all ordered extents to complete first. This issue happened often when running the fstest btrfs/088 and it's easy to trigger it by running in a loop until the panic happens: for ((i = 1; i <= 10000; i++)) do ./check btrfs/088 ; done [17156.862573] BTRFS critical (device sdc): panic in ordered_data_tree_panic:70: Inconsistency in ordered tree at offset 0 (errno=-17 Object already exists) [17156.864052] ------------[ cut here ]------------ [17156.864052] kernel BUG at fs/btrfs/ordered-data.c:70! (...) [17156.864052] Call Trace: [17156.864052] [<ffffffffa03876e3>] btrfs_add_ordered_extent+0x12/0x14 [btrfs] [17156.864052] [<ffffffffa03787e2>] run_delalloc_nocow+0x5bf/0x747 [btrfs] [17156.864052] [<ffffffffa03789ff>] run_delalloc_range+0x95/0x353 [btrfs] [17156.864052] [<ffffffffa038b7fe>] writepage_delalloc.isra.16+0xb9/0x13f [btrfs] [17156.864052] [<ffffffffa038d75b>] __extent_writepage+0x129/0x1f7 [btrfs] [17156.864052] [<ffffffffa038da5a>] extent_write_cache_pages.isra.15.constprop.28+0x231/0x2f4 [btrfs] [17156.864052] [<ffffffff810ad2af>] ? __module_text_address+0x12/0x59 [17156.864052] [<ffffffff8107d33d>] ? trace_hardirqs_on+0xd/0xf [17156.864052] [<ffffffffa038df76>] extent_writepages+0x4b/0x5c [btrfs] [17156.864052] [<ffffffff81144431>] ? kmem_cache_free+0x9b/0xce [17156.864052] [<ffffffffa0376a46>] ? btrfs_submit_direct+0x3fc/0x3fc [btrfs] [17156.864052] [<ffffffffa0389cd6>] ? free_extent_state+0x8c/0xc1 [btrfs] [17156.864052] [<ffffffffa0374871>] btrfs_writepages+0x28/0x2a [btrfs] [17156.864052] [<ffffffff8110c4c8>] do_writepages+0x23/0x2c [17156.864052] [<ffffffff81102f36>] __filemap_fdatawrite_range+0x5a/0x61 [17156.864052] [<ffffffff81102f6e>] filemap_fdatawrite_range+0x13/0x15 [17156.864052] [<ffffffffa0383ef7>] btrfs_fdatawrite_range+0x21/0x48 [btrfs] [17156.864052] [<ffffffffa03ab89e>] __btrfs_write_out_cache.isra.14+0x2d9/0x3a7 [btrfs] [17156.864052] [<ffffffffa03ac1ab>] ? btrfs_write_out_cache+0x41/0xdc [btrfs] [17156.864052] [<ffffffffa03ac1fd>] btrfs_write_out_cache+0x93/0xdc [btrfs] [17156.864052] [<ffffffffa0363847>] ? btrfs_start_dirty_block_groups+0x13a/0x2b2 [btrfs] [17156.864052] [<ffffffffa03638e6>] btrfs_start_dirty_block_groups+0x1d9/0x2b2 [btrfs] [17156.864052] [<ffffffff8107d33d>] ? trace_hardirqs_on+0xd/0xf [17156.864052] [<ffffffffa037209e>] btrfs_commit_transaction+0x130/0x9c9 [btrfs] [17156.864052] [<ffffffffa034c748>] btrfs_sync_fs+0xe1/0x12d [btrfs] Signed-off-by: NFilipe Manana <fdmanana@suse.com> Signed-off-by: NChris Mason <clm@fb.com>
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