# git rev-parse -q --verify 6c44be1b8e2d8c0161ac39d5d39ea4dff39da71c^{commit}
6c44be1b8e2d8c0161ac39d5d39ea4dff39da71c
already have revision, skipping fetch
# git checkout -q -f -B kisskb 6c44be1b8e2d8c0161ac39d5d39ea4dff39da71c
# git clean -qxdf
# < git log -1
# commit 6c44be1b8e2d8c0161ac39d5d39ea4dff39da71c
# Author: Nathan Lynch <nathanl@linux.ibm.com>
# Date:   Fri Oct 15 12:39:02 2021 -0500
# 
#     powerpc/smp: do not decrement idle task preempt count in CPU offline
#     
#     With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we
#     get:
#     
#     BUG: scheduling while atomic: swapper/1/0/0x00000000
#     no locks held by swapper/1/0.
#     CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100
#     Call Trace:
#      dump_stack_lvl+0xac/0x108
#      __schedule_bug+0xac/0xe0
#      __schedule+0xcf8/0x10d0
#      schedule_idle+0x3c/0x70
#      do_idle+0x2d8/0x4a0
#      cpu_startup_entry+0x38/0x40
#      start_secondary+0x2ec/0x3a0
#      start_secondary_prolog+0x10/0x14
#     
#     This is because powerpc's arch_cpu_idle_dead() decrements the idle task's
#     preempt count, for reasons explained in commit a7c2bb8279d2 ("powerpc:
#     Re-enable preemption before cpu_die()"), specifically "start_secondary()
#     expects a preempt_count() of 0."
#     
#     However, since commit 2c669ef6979c ("powerpc/preempt: Don't touch the idle
#     task's preempt_count during hotplug") and commit f1a0a376ca0c ("sched/core:
#     Initialize the idle task with preemption disabled"), that justification no
#     longer holds.
#     
#     The idle task isn't supposed to re-enable preemption, so remove the
#     vestigial preempt_enable() from the CPU offline path.
#     
#     Tested with pseries and powernv in qemu, and pseries on PowerVM.
#     
#     Fixes: 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug")
#     Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
#     Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/20211015173902.2278118-1-nathanl@linux.ibm.com
# < /opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 6c44be1b8e2d8c0161ac39d5d39ea4dff39da71c
# < make -s -j 8 ARCH=powerpc O=/kisskb/build/powerpc-fixes_pseries_defconfig+NO_MEMORY_HOTREMOVE_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  pseries_defconfig
# Added to kconfig CONFIG_MEMORY_HOTPLUG=y
# Added to kconfig CONFIG_MEMORY_HOTREMOVE=n
# < make -s -j 8 ARCH=powerpc O=/kisskb/build/powerpc-fixes_pseries_defconfig+NO_MEMORY_HOTREMOVE_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 8 ARCH=powerpc O=/kisskb/build/powerpc-fixes_pseries_defconfig+NO_MEMORY_HOTREMOVE_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
# make -s -j 8 ARCH=powerpc O=/kisskb/build/powerpc-fixes_pseries_defconfig+NO_MEMORY_HOTREMOVE_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_pseries_defconfig+NO_MEMORY_HOTREMOVE_powerpc-gcc9
# Build took: 0:06:07.792407