[bug report] Potential atomicity bug in fs/btrfs/compression.c, between btrfs_put_workspace() and free_workspace_manager()

[Ginger]

Dear Linux kernel maintainers,

My research-based static analyzer found a potential atomicity bug
within the 'fs/btrfs' subsystem, more specifically, in
'fs/btrfs/compression.c'.

Kernel version: long-term kernel v6.18.9

Potential concurrent triggering executions:
T0:
btrfs_put_workspace
     --> ws_lock = fs_info->compr_wsm[type]->ws_lock;
     --> spin_lock(ws_lock)
     --> list_add(ws, gwsm->idl_ws)
     --> spin_unlock(ws_lock)

T1:
free_workspace_manager
    --> gwsm = fs_info->compr_wsm[type];
    -->  while(!list_empty(gwsm->idle_ws))

In T1, the accesses to the idle_ws are plain memory reads and writes,
without holding the 'ws_lock' to protect against potential data races.

Please kindly check at your convenience. Thank you for your time and
consideration.

Best regards,
Ginger