# git rev-parse -q --verify b6fbf9e64995137a57c19b0aa7f6c76c727439dc^{commit}
b6fbf9e64995137a57c19b0aa7f6c76c727439dc
already have revision, skipping fetch
# git checkout -q -f -B kisskb b6fbf9e64995137a57c19b0aa7f6c76c727439dc
# git clean -qxdf
# git log -1
commit b6fbf9e64995137a57c19b0aa7f6c76c727439dc
Author: Alistair Popple <alistair@popple.id.au>
Date:   Fri Mar 2 16:18:45 2018 +1100

    powerpc/powernv/npu: Fix deadlock in mmio_invalidate()
    
    When sending TLB invalidates to the NPU we need to send extra flushes due
    to a hardware issue. The original implementation would lock the all the
    ATSD MMIO registers sequentially before unlocking and relocking each of
    them sequentially to do the extra flush.
    
    This introduced a deadlock as it is possible for one thread to hold one
    ATSD register whilst waiting for another register to be freed while the
    other thread is holding that register waiting for the one in the first
    thread to be freed.
    
    For example if there are two threads and two ATSD registers:
    
      Thread A	Thread B
      ----------------------
      Acquire 1
      Acquire 2
      Release 1	Acquire 1
      Wait 1	Wait 2
    
    Both threads will be stuck waiting to acquire a register resulting in an
    RCU stall warning or soft lockup.
    
    This patch solves the deadlock by refactoring the code to ensure registers
    are not released between flushes and to ensure all registers are either
    acquired or released together and in order.
    
    Fixes: bbd5ff50afff ("powerpc/powernv/npu-dma: Add explicit flush when sending an ATSD")
    Signed-off-by: Alistair Popple <alistair@popple.id.au>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
# < /opt/cross/kisskb/gcc-5.2.0-nolibc/powerpc64le-linux/bin/powerpc64le-linux-gcc --version
# < git log --format=%s --max-count=1 b6fbf9e64995137a57c19b0aa7f6c76c727439dc
# < make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-next_allmodconfig+ppc64le_ppc64le CROSS_COMPILE=/opt/cross/kisskb/gcc-5.2.0-nolibc/powerpc64le-linux/bin/powerpc64le-linux-  allmodconfig
# Added to kconfig CONFIG_CPU_LITTLE_ENDIAN=y
# Added to kconfig CONFIG_BUILD_DOCSRC=n
# Added to kconfig CONFIG_MODULE_SIG=n
# Added to kconfig CONFIG_SAMPLES=n
# yes \n | make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-next_allmodconfig+ppc64le_ppc64le CROSS_COMPILE=/opt/cross/kisskb/gcc-5.2.0-nolibc/powerpc64le-linux/bin/powerpc64le-linux-  oldconfig
yes: standard output: Broken pipe
yes: write error
# make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-next_allmodconfig+ppc64le_ppc64le CROSS_COMPILE=/opt/cross/kisskb/gcc-5.2.0-nolibc/powerpc64le-linux/bin/powerpc64le-linux-  
In file included from /kisskb/src/include/linux/io.h:25:0,
                 from /kisskb/src/include/linux/of_address.h:7,
                 from /kisskb/src/drivers/ata/ahci_qoriq.c:18:
/kisskb/src/drivers/ata/ahci_qoriq.c: In function 'ahci_qoriq_hardreset':
/kisskb/src/arch/powerpc/include/asm/io.h:162:2: warning: 'px_is' may be used uninitialized in this function [-Wmaybe-uninitialized]
  __asm__ __volatile__("sync;"#insn"%U0%X0 %1,%0"   \
  ^
/kisskb/src/drivers/ata/ahci_qoriq.c:86:14: note: 'px_is' was declared here
  u32 px_cmd, px_is, px_val;
              ^
In file included from /kisskb/src/include/linux/io.h:25:0,
                 from /kisskb/src/include/linux/of_address.h:7,
                 from /kisskb/src/drivers/ata/ahci_qoriq.c:18:
/kisskb/src/arch/powerpc/include/asm/io.h:162:2: warning: 'px_cmd' may be used uninitialized in this function [-Wmaybe-uninitialized]
  __asm__ __volatile__("sync;"#insn"%U0%X0 %1,%0"   \
  ^
/kisskb/src/drivers/ata/ahci_qoriq.c:86:6: note: 'px_cmd' was declared here
  u32 px_cmd, px_is, px_val;
      ^
/kisskb/src/drivers/input/joystick/analog.c:176:2: warning: #warning Precise timer not defined for this architecture. [-Wcpp]
 #warning Precise timer not defined for this architecture.
  ^
WARNING: vmlinux.o(.text+0x35f0): Section mismatch in reference from the variable __boot_from_prom to the function .init.text:prom_init()
The function __boot_from_prom() references
the function __init prom_init().
This is often because __boot_from_prom lacks a __init 
annotation or the annotation of prom_init is wrong.

WARNING: vmlinux.o(.text+0x3844): Section mismatch in reference from the variable start_here_multiplatform to the function .init.text:early_setup()
The function start_here_multiplatform() references
the function __init early_setup().
This is often because start_here_multiplatform lacks a __init 
annotation or the annotation of early_setup is wrong.

WARNING: vmlinux.o(.text+0x3878): Section mismatch in reference from the variable start_here_common to the function .init.text:start_kernel()
The function start_here_common() references
the function __init start_kernel().
This is often because start_here_common lacks a __init 
annotation or the annotation of start_kernel is wrong.

WARNING: vmlinux.o(.text+0x79cf0): Section mismatch in reference from the function stop_machine_change_mapping() to the function .meminit.text:create_physical_mapping()
The function stop_machine_change_mapping() references
the function __meminit create_physical_mapping().
This is often because stop_machine_change_mapping lacks a __meminit 
annotation or the annotation of create_physical_mapping is wrong.

WARNING: vmlinux.o(.text+0x79cfc): Section mismatch in reference from the function stop_machine_change_mapping() to the function .meminit.text:create_physical_mapping()
The function stop_machine_change_mapping() references
the function __meminit create_physical_mapping().
This is often because stop_machine_change_mapping lacks a __meminit 
annotation or the annotation of create_physical_mapping is wrong.

Completed OK
# rm -rf /kisskb/build/powerpc-next_allmodconfig+ppc64le_ppc64le
# Build took: 0:12:29.175894