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Work queues cannot be allocated when a mutex is held because the mutex
may be in use and that would make it sleep. Doing so generates the
following splat with 4.13+:
[ 19.513298] ======================================================
[ 19.513429] WARNING: possible circular locking dependency detected
[ 19.513557] 4.13.0-rc5+ #6 Not tainted
[ 19.513638] ------------------------------------------------------
[ 19.513767] cpuhp/0/12 is trying to acquire lock:
[ 19.513867] (&tz->lock){+.+.+.}, at: [<ffffffff924afebb>] thermal_zone_get_temp+0x5b/0xb0
[ 19.514047]
[ 19.514047] but task is already holding lock:
[ 19.514166] (cpuhp_state){+.+.+.}, at: [<ffffffff91cc4baa>] cpuhp_thread_fun+0x3a/0x210
[ 19.514338]
[ 19.514338] which lock already depends on the new lock.
This lock dependency already existed with previous kernel versions,
but it was not detected until commit 49dfe2a677 ("cpuhotplug: Link
lock stacks for hotplug callbacks") was introduced.
Reported-by: David Weinehall <david.weinehall@intel.com>
Reported-by: Jiri Kosina <jikos@kernel.org>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.