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[ Upstream commit fd888e85fe ]
The writer acquires dev_base_lock with disabled bottom halves.
The reader can acquire dev_base_lock without disabling bottom halves
because there is no writer in softirq context.
On PREEMPT_RT the softirqs are preemptible and local_bh_disable() acts
as a lock to ensure that resources, that are protected by disabling
bottom halves, remain protected.
This leads to a circular locking dependency if the lock acquired with
disabled bottom halves (as in write_lock_bh()) and somewhere else with
enabled bottom halves (as by read_lock() in netstat_show()) followed by
disabling bottom halves (cxgb_get_stats() -> t4_wr_mbox_meat_timeout()
-> spin_lock_bh()). This is the reverse locking order.
All read_lock() invocation are from sysfs callback which are not invoked
from softirq context. Therefore there is no need to disable bottom
halves while acquiring a write lock.
Acquire the write lock of dev_base_lock without disabling bottom halves.
Reported-by: Pei Zhang <pezhang@redhat.com>
Reported-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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.