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Commit851a723e45("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") added a kfree() call to free any user provided affinity mask, if present. It was changed later to use kfree_rcu() in commit9a5418bc48("sched/core: Use kfree_rcu() in do_set_cpus_allowed()") to avoid a circular locking dependency problem. It turns out that even kfree_rcu() isn't safe for avoiding circular locking problem. As reported by kernel test robot, the following circular locking dependency now exists: &rdp->nocb_lock --> rcu_node_0 --> &rq->__lock Solve this by breaking the rcu_node_0 --> &rq->__lock chain by moving the resched_cpu() out from under rcu_node lock. [peterz: heavily borrowed from Waiman's Changelog] [paulmck: applied Z qiang feedback] Fixes:851a723e45("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") Reported-by: kernel test robot <oliver.sang@intel.com> Acked-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/oe-lkp/202310302207.a25f1a30-oliver.sang@intel.com Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@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.