linux-kernel - [PATCH v6 0/2] Implement reentrant rtas call

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Message-Id: <20200518234245.200672-1-leobras.c@gmail.com>
Date:   Mon, 18 May 2020 20:42:43 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Leonardo Bras <leobras.c@...il.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Nadav Amit <namit@...are.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH v6 0/2] Implement reentrant rtas call

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@...il.com>

Special thanks to Nick Piggin, who have been helping me a lot with
this series!

---
Changes since v5:
- Renames new paca member from reentrant_args to rtas_args_reentrant
- Compile out rtas_args_reentrant if CONFIG_PPC_RTAS=n
- new_rtas_args() is skipped (returns NULL) if CPU_FTR_HVMODE

Changes since v4:
- Insted of having the full buffer on PACA, adds only a pointer and
  allocate it during allocate_paca(), making sure it's in a memory
  range available for RTAS (32-bit). (Thanks Nick Piggin!)

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

-- 
2.25.4