erofs: fix deadlock when shrink erofs slab
We observed the following deadlock in the stress test under low memory scenario: Thread A Thread B - erofs_shrink_scan - erofs_try_to_release_workgroup - erofs_workgroup_try_to_freeze -- A - z_erofs_do_read_page - z_erofs_collection_begin - z_erofs_register_collection - erofs_insert_workgroup - xa_lock(&sbi->managed_pslots) -- B - erofs_workgroup_get - erofs_wait_on_workgroup_freezed -- A - xa_erase - xa_lock(&sbi->managed_pslots) -- B To fix this, it needs to hold xa_lock before freezing the workgroup since xarray will be touched then. So let's hold the lock before accessing each workgroup, just like what we did with the radix tree before. [ Gao Xiang: Jianhua Hao also reports this issue at https://lore.kernel.org/r/b10b85df30694bac8aadfe43537c897a@xiaomi.com ] Link: https://lore.kernel.org/r/20211118135844.3559-1-huangjianan@oppo.com Fixes: 64094a04 ("erofs: convert workstn to XArray") Reviewed-by: Chao Yu <chao@kernel.org> Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com> Signed-off-by: Huang Jianan <huangjianan@oppo.com> Reported-by: Jianhua Hao <haojianhua1@xiaomi.com> Signed-off-by: Gao Xiang <xiang@kernel.org>
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