044d0d6de9
Problem:
raw_local_irq_save(); // software state on
local_irq_save(); // software state off
...
local_irq_restore(); // software state still off, because we don't enable IRQs
raw_local_irq_restore(); // software state still off, *whoopsie*
existing instances:
- lock_acquire()
raw_local_irq_save()
__lock_acquire()
arch_spin_lock(&graph_lock)
pv_wait() := kvm_wait() (same or worse for Xen/HyperV)
local_irq_save()
- trace_clock_global()
raw_local_irq_save()
arch_spin_lock()
pv_wait() := kvm_wait()
local_irq_save()
- apic_retrigger_irq()
raw_local_irq_save()
apic->send_IPI() := default_send_IPI_single_phys()
local_irq_save()
Possible solutions:
A) make it work by enabling the tracing inside raw_*()
B) make it work by keeping tracing disabled inside raw_*()
C) call it broken and clean it up now
Now, given that the only reason to use the raw_* variant is because you don't
want tracing. Therefore A) seems like a weird option (although it can be done).
C) is tempting, but OTOH it ends up converting a _lot_ of code to raw just
because there is one raw user, this strips the validation/tracing off for all
the other users.
So we pick B) and declare any code that ends up doing:
raw_local_irq_save()
local_irq_save()
lockdep_assert_irqs_disabled();
broken. AFAICT this problem has existed forever, the only reason it came
up is because commit: 859d069ee1 ("lockdep: Prepare for NMI IRQ
state tracking") changed IRQ tracing vs lockdep recursion and the
first instance is fairly common, the other cases hardly ever happen.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[rewrote changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Marco Elver <elver@google.com>
Link: https://lkml.kernel.org/r/20200723105615.1268126-1-npiggin@gmail.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.