Revision 787252a10d9422f3058df9a4821f389e5326c440 authored by Nathan Lynch on 15 October 2021, 17:39:02 UTC, committed by Michael Ellerman on 20 October 2021, 10:38:01 UTC
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> Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20211015173902.2278118-1-nathanl@linux.ibm.com
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Kbuild
# SPDX-License-Identifier: GPL-2.0
#
# Kbuild for top-level directory of the kernel
#####
# Generate bounds.h
bounds-file := include/generated/bounds.h
always-y := $(bounds-file)
targets := kernel/bounds.s
$(bounds-file): kernel/bounds.s FORCE
$(call filechk,offsets,__LINUX_BOUNDS_H__)
#####
# Generate timeconst.h
timeconst-file := include/generated/timeconst.h
filechk_gentimeconst = echo $(CONFIG_HZ) | bc -q $<
$(timeconst-file): kernel/time/timeconst.bc FORCE
$(call filechk,gentimeconst)
#####
# Generate asm-offsets.h
offsets-file := include/generated/asm-offsets.h
always-y += $(offsets-file)
targets += arch/$(SRCARCH)/kernel/asm-offsets.s
arch/$(SRCARCH)/kernel/asm-offsets.s: $(timeconst-file) $(bounds-file)
$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE
$(call filechk,offsets,__ASM_OFFSETS_H__)
#####
# Check for missing system calls
always-y += missing-syscalls
quiet_cmd_syscalls = CALL $<
cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE
$(call cmd,syscalls)
#####
# Check atomic headers are up-to-date
always-y += old-atomics
quiet_cmd_atomics = CALL $<
cmd_atomics = $(CONFIG_SHELL) $<
old-atomics: scripts/atomic/check-atomics.sh FORCE
$(call cmd,atomics)
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