e6829d1bd3
Lockdep reports the following deadlock scenarios for CXL root device
power-management, device_prepare(), operations, and device_shutdown()
operations for 'nd_region' devices:
Chain exists of:
&nvdimm_region_key --> &nvdimm_bus->reconfig_mutex --> system_transition_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(system_transition_mutex);
lock(&nvdimm_bus->reconfig_mutex);
lock(system_transition_mutex);
lock(&nvdimm_region_key);
Chain exists of:
&cxl_nvdimm_bridge_key --> acpi_scan_lock --> &cxl_root_key
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&cxl_root_key);
lock(acpi_scan_lock);
lock(&cxl_root_key);
lock(&cxl_nvdimm_bridge_key);
These stem from holding nvdimm_bus_lock() over hibernate_quiet_exec()
which walks the entire system device topology taking device_lock() along
the way. The nvdimm_bus_lock() is protecting against unregistration,
multiple simultaneous ops callers, and preventing activate_show() from
racing activate_store(). For the first 2, the lock is redundant.
Unregistration already flushes all ops users, and sysfs already prevents
multiple threads to be active in an ops handler at the same time. For
the last userspace should already be waiting for its last
activate_store() to complete, and does not need activate_show() to flush
the write side, so this lock usage can be deleted in these attributes.
Fixes: 48001ea50d17 ("PM, libnvdimm: Add runtime firmware activation support")
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/165074883800.4116052.10737040861825806582.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.