d8797b1257
__install_bp_hardening_cb() is called via stop_machine() as part of the cpu_enable callback. To force each CPU to take its turn when allocating slots, they take a spinlock. With the RT patches applied, the spinlock becomes a mutex, and we get warnings about sleeping while in stop_machine(): | [ 0.319176] CPU features: detected: RAS Extension Support | [ 0.319950] BUG: scheduling while atomic: migration/3/36/0x00000002 | [ 0.319955] Modules linked in: | [ 0.319958] Preemption disabled at: | [ 0.319969] [<ffff000008181ae4>] cpu_stopper_thread+0x7c/0x108 | [ 0.319973] CPU: 3 PID: 36 Comm: migration/3 Not tainted 4.19.1-rt3-00250-g330fc2c2a880 #2 | [ 0.319975] Hardware name: linux,dummy-virt (DT) | [ 0.319976] Call trace: | [ 0.319981] dump_backtrace+0x0/0x148 | [ 0.319983] show_stack+0x14/0x20 | [ 0.319987] dump_stack+0x80/0xa4 | [ 0.319989] __schedule_bug+0x94/0xb0 | [ 0.319991] __schedule+0x510/0x560 | [ 0.319992] schedule+0x38/0xe8 | [ 0.319994] rt_spin_lock_slowlock_locked+0xf0/0x278 | [ 0.319996] rt_spin_lock_slowlock+0x5c/0x90 | [ 0.319998] rt_spin_lock+0x54/0x58 | [ 0.320000] enable_smccc_arch_workaround_1+0xdc/0x260 | [ 0.320001] __enable_cpu_capability+0x10/0x20 | [ 0.320003] multi_cpu_stop+0x84/0x108 | [ 0.320004] cpu_stopper_thread+0x84/0x108 | [ 0.320008] smpboot_thread_fn+0x1e8/0x2b0 | [ 0.320009] kthread+0x124/0x128 | [ 0.320010] ret_from_fork+0x10/0x18 Switch this to a raw spinlock, as we know this is only called with IRQs masked. Signed-off-by: James Morse <james.morse@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.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.