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1378a68344
dcssblk_remove_store() holds the dcssblk_devices_sem semaphore while calling device_unregister(), which in turn tries to acquire the kernfs kn->dev_map rwsem for the device sysfs subtree. The same rwsem is also acquired when using the per-device sysfs attributes in the device sub-tree, and the attribute handlers then also acquire the dcssblk_devices_sem. This can lead to a deadlock when removing a DCSS while concurrently reading from / writing to one of its sysfs attributes. The following lockdep warning hinted towards the issue (CPU0 = dcssblk_remove_store, CPU1 = dcssblk_shared_store): [ 76.496047] Possible unsafe locking scenario: [ 76.496054] CPU0 CPU1 [ 76.496059] ---- ---- [ 76.496087] lock(&dcssblk_devices_sem); [ 76.496090] lock(s_active#175); [ 76.496106] lock(&dcssblk_devices_sem); [ 76.496110] lock(s_active#175); [ 76.496115] *** DEADLOCK *** Fix this by releasing the dcssblk_devices_sem semaphore, which only protects internal DCSS data, before calling device_unregister(). Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> |
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