On Fri, Apr 24, 2020 at 04:05:32PM -0700, Suraj Jitindar Singh wrote:
From: kaixuxia <xiakaixu1987@xxxxxxxxx> commit bc56ad8c74b8588685c2875de0df8ab6974828ef upstream. When performing rename operation with RENAME_WHITEOUT flag, we will hold AGF lock to allocate or free extents in manipulating the dirents firstly, and then doing the xfs_iunlink_remove() call last to hold AGI lock to modify the tmpfile info, so we the lock order AGI->AGF. The big problem here is that we have an ordering constraint on AGF and AGI locking - inode allocation locks the AGI, then can allocate a new extent for new inodes, locking the AGF after the AGI. Hence the ordering that is imposed by other parts of the code is AGI before AGF. So we get an ABBA deadlock between the AGI and AGF here. Process A: Call trace: ? __schedule+0x2bd/0x620 schedule+0x33/0x90 schedule_timeout+0x17d/0x290 __down_common+0xef/0x125 ? xfs_buf_find+0x215/0x6c0 [xfs] down+0x3b/0x50 xfs_buf_lock+0x34/0xf0 [xfs] xfs_buf_find+0x215/0x6c0 [xfs] xfs_buf_get_map+0x37/0x230 [xfs] xfs_buf_read_map+0x29/0x190 [xfs] xfs_trans_read_buf_map+0x13d/0x520 [xfs] xfs_read_agf+0xa6/0x180 [xfs] ? schedule_timeout+0x17d/0x290 xfs_alloc_read_agf+0x52/0x1f0 [xfs] xfs_alloc_fix_freelist+0x432/0x590 [xfs] ? down+0x3b/0x50 ? xfs_buf_lock+0x34/0xf0 [xfs] ? xfs_buf_find+0x215/0x6c0 [xfs] xfs_alloc_vextent+0x301/0x6c0 [xfs] xfs_ialloc_ag_alloc+0x182/0x700 [xfs] ? _xfs_trans_bjoin+0x72/0xf0 [xfs] xfs_dialloc+0x116/0x290 [xfs] xfs_ialloc+0x6d/0x5e0 [xfs] ? xfs_log_reserve+0x165/0x280 [xfs] xfs_dir_ialloc+0x8c/0x240 [xfs] xfs_create+0x35a/0x610 [xfs] xfs_generic_create+0x1f1/0x2f0 [xfs] ... Process B: Call trace: ? __schedule+0x2bd/0x620 ? xfs_bmapi_allocate+0x245/0x380 [xfs] schedule+0x33/0x90 schedule_timeout+0x17d/0x290 ? xfs_buf_find+0x1fd/0x6c0 [xfs] __down_common+0xef/0x125 ? xfs_buf_get_map+0x37/0x230 [xfs] ? xfs_buf_find+0x215/0x6c0 [xfs] down+0x3b/0x50 xfs_buf_lock+0x34/0xf0 [xfs] xfs_buf_find+0x215/0x6c0 [xfs] xfs_buf_get_map+0x37/0x230 [xfs] xfs_buf_read_map+0x29/0x190 [xfs] xfs_trans_read_buf_map+0x13d/0x520 [xfs] xfs_read_agi+0xa8/0x160 [xfs] xfs_iunlink_remove+0x6f/0x2a0 [xfs] ? current_time+0x46/0x80 ? xfs_trans_ichgtime+0x39/0xb0 [xfs] xfs_rename+0x57a/0xae0 [xfs] xfs_vn_rename+0xe4/0x150 [xfs] ... In this patch we move the xfs_iunlink_remove() call to before acquiring the AGF lock to preserve correct AGI/AGF locking order. Signed-off-by: kaixuxia <kaixuxia@xxxxxxxxxxx> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx> Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> Minor massage required to backport to apply due to removal of out_bmap_cancel: error path label upstream as a result of code rework. Only change was to the last code block removed by the patch. Functionally equivalent to upstream.
This patch also needs to be backported to 4.19. I can look into that tomorrow unless you can send a patch sooner :) -- Thanks, Sasha
