[PATCH v4 0/2] Implement reentrant rtas call

From: Leonardo Bras
Date: Thu May 14 2020 - 19:53:04 EST


Patch 2 implement rtas_call_reentrant() for reentrant rtas-calls:
"ibm,int-on", "ibm,int-off",ibm,get-xive" and "ibm,set-xive",
according to LoPAPR Version 1.1 (March 24, 2016).

For that, it's necessary that every call uses a different
rtas buffer (rtas_args). Paul Mackerras suggested using the PACA
structure for creating a per-cpu buffer for these calls.

Patch 1 was necessary to make PACA have a 'struct rtas_args' member.

Reentrant rtas calls can be useful to avoid deadlocks in crashing,
where rtas-calls are needed, but some other thread crashed holding
the rtas.lock.

This is a backtrace of a deadlock from a kdump testing environment:

#0 arch_spin_lock
#1 lock_rtas ()
#2 rtas_call (token=8204, nargs=1, nret=1, outputs=0x0)
#3 ics_rtas_mask_real_irq (hw_irq=4100)
#4 machine_kexec_mask_interrupts
#5 default_machine_crash_shutdown
#6 machine_crash_shutdown
#7 __crash_kexec
#8 crash_kexec
#9 oops_end

Signed-off-by: Leonardo Bras <leobras.c@xxxxxxxxx>

---
Changes since v3:
- Adds protection from preemption and interruption

Changes since v2:
- Fixed build failure from ppc64e, by including spinlock_types.h on
rtas-types.h
- Improved commit messages

Changes since v1:
- Moved buffer from stack to PACA (as suggested by Paul Mackerras)
- Added missing output bits
- Improve documentation following kernel-doc format (as suggested by
Nathan Lynch)


Leonardo Bras (2):
powerpc/rtas: Move type/struct definitions from rtas.h into
rtas-types.h
powerpc/rtas: Implement reentrant rtas call

arch/powerpc/include/asm/paca.h | 2 +
arch/powerpc/include/asm/rtas-types.h | 126 ++++++++++++++++++++++++++
arch/powerpc/include/asm/rtas.h | 119 +-----------------------
arch/powerpc/kernel/rtas.c | 42 +++++++++
arch/powerpc/sysdev/xics/ics-rtas.c | 22 ++---
5 files changed, 183 insertions(+), 128 deletions(-)
create mode 100644 arch/powerpc/include/asm/rtas-types.h

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