Hi Baokun, On 2024/3/7 10:44, Baokun Li wrote:
Lockdep reported the following issue when mounting erofs with a domain_id:============================================ WARNING: possible recursive locking detected 6.8.0-rc7-xfstests #521 Not tainted -------------------------------------------- mount/396 is trying to acquire lock: ffff907a8aaaa0e0 (&type->s_umount_key#50/1){+.+.}-{3:3}, at: alloc_super+0xe3/0x3d0 but task is already holding lock: ffff907a8aaa90e0 (&type->s_umount_key#50/1){+.+.}-{3:3}, at: alloc_super+0xe3/0x3d0 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&type->s_umount_key#50/1); lock(&type->s_umount_key#50/1); *** DEADLOCK *** May be due to missing lock nesting notation 2 locks held by mount/396: #0: ffff907a8aaa90e0 (&type->s_umount_key#50/1){+.+.}-{3:3}, at: alloc_super+0xe3/0x3d0 #1: ffffffffc00e6f28 (erofs_domain_list_lock){+.+.}-{3:3}, at: erofs_fscache_register_fs+0x3d/0x270 [erofs] stack backtrace: CPU: 1 PID: 396 Comm: mount Not tainted 6.8.0-rc7-xfstests #521 Call Trace: <TASK> dump_stack_lvl+0x64/0xb0 validate_chain+0x5c4/0xa00 __lock_acquire+0x6a9/0xd50 lock_acquire+0xcd/0x2b0 down_write_nested+0x45/0xd0 alloc_super+0xe3/0x3d0 sget_fc+0x62/0x2f0 vfs_get_super+0x21/0x90 vfs_get_tree+0x2c/0xf0 fc_mount+0x12/0x40 vfs_kern_mount.part.0+0x75/0x90 kern_mount+0x24/0x40 erofs_fscache_register_fs+0x1ef/0x270 [erofs] erofs_fc_fill_super+0x213/0x380 [erofs] This is because the file_system_type of both erofs and the pseudo-mount point of domain_id is erofs_fs_type, so two successive calls to alloc_super() are considered to be using the same lock and trigger the warning above. Therefore add a nodev file_system_type named erofs_anon_fs_type to silence this complaint. In addition, to reduce code coupling, refactor out the erofs_anon_init_fs_context() and erofs_kill_pseudo_sb() functions and move the erofs_pseudo_mnt related code to fscache.c. Signed-off-by: Baokun Li <[email protected]>
IMHO, in the beginning, I'd like to avoid introducing another fs type for erofs to share (meta)data between filesystems since it will cause churn, could we use some alternative way to resolve this? Or Jingbo might have some other ideas? Thanks, Gao Xiang
