mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-11-25 03:00:53 +07:00
b4282c7920
Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: There isn't much to be done here: just mark the document title as such and add a :Author:. While here, use upper case at the beginning of a few paragraphs that start with lower case. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
53 lines
2.3 KiB
Plaintext
53 lines
2.3 KiB
Plaintext
=======================
|
|
IRQ-flags state tracing
|
|
=======================
|
|
|
|
:Author: started by Ingo Molnar <mingo@redhat.com>
|
|
|
|
The "irq-flags tracing" feature "traces" hardirq and softirq state, in
|
|
that it gives interested subsystems an opportunity to be notified of
|
|
every hardirqs-off/hardirqs-on, softirqs-off/softirqs-on event that
|
|
happens in the kernel.
|
|
|
|
CONFIG_TRACE_IRQFLAGS_SUPPORT is needed for CONFIG_PROVE_SPIN_LOCKING
|
|
and CONFIG_PROVE_RW_LOCKING to be offered by the generic lock debugging
|
|
code. Otherwise only CONFIG_PROVE_MUTEX_LOCKING and
|
|
CONFIG_PROVE_RWSEM_LOCKING will be offered on an architecture - these
|
|
are locking APIs that are not used in IRQ context. (the one exception
|
|
for rwsems is worked around)
|
|
|
|
Architecture support for this is certainly not in the "trivial"
|
|
category, because lots of lowlevel assembly code deal with irq-flags
|
|
state changes. But an architecture can be irq-flags-tracing enabled in a
|
|
rather straightforward and risk-free manner.
|
|
|
|
Architectures that want to support this need to do a couple of
|
|
code-organizational changes first:
|
|
|
|
- add and enable TRACE_IRQFLAGS_SUPPORT in their arch level Kconfig file
|
|
|
|
and then a couple of functional changes are needed as well to implement
|
|
irq-flags-tracing support:
|
|
|
|
- in lowlevel entry code add (build-conditional) calls to the
|
|
trace_hardirqs_off()/trace_hardirqs_on() functions. The lock validator
|
|
closely guards whether the 'real' irq-flags matches the 'virtual'
|
|
irq-flags state, and complains loudly (and turns itself off) if the
|
|
two do not match. Usually most of the time for arch support for
|
|
irq-flags-tracing is spent in this state: look at the lockdep
|
|
complaint, try to figure out the assembly code we did not cover yet,
|
|
fix and repeat. Once the system has booted up and works without a
|
|
lockdep complaint in the irq-flags-tracing functions arch support is
|
|
complete.
|
|
- if the architecture has non-maskable interrupts then those need to be
|
|
excluded from the irq-tracing [and lock validation] mechanism via
|
|
lockdep_off()/lockdep_on().
|
|
|
|
In general there is no risk from having an incomplete irq-flags-tracing
|
|
implementation in an architecture: lockdep will detect that and will
|
|
turn itself off. I.e. the lock validator will still be reliable. There
|
|
should be no crashes due to irq-tracing bugs. (except if the assembly
|
|
changes break other code by modifying conditions or registers that
|
|
shouldn't be)
|
|
|