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linux-stable/arch/powerpc
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Nathan Lynch 787252a10d 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 a7c2bb8279 ("powerpc:
Re-enable preemption before cpu_die()"), specifically "start_secondary()
expects a preempt_count() of 0."

However, since commit 2c669ef697 ("powerpc/preempt: Don't touch the idle
task's preempt_count during hotplug") and commit f1a0a376ca ("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: 2c669ef697 ("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
2021-10-20 21:38:01 +11:00
..
boot powerpc/boot: Fix build failure since GCC 4.9 removal 2021-09-14 08:33:32 -07:00
configs powerpc/configs/microwatt: Enable options for systemd 2021-08-27 00:56:53 +10:00
crypto crypto: powepc/sha1 - remove unneeded semicolon 2021-03-07 15:13:14 +11:00
include powerpc/32s: Fix kuap_kernel_restore() 2021-10-07 23:34:00 +11:00
kernel powerpc/smp: do not decrement idle task preempt count in CPU offline 2021-10-20 21:38:01 +11:00
kexec powerpc updates for 5.15 2021-09-03 11:22:50 -07:00
kvm KVM: PPC: Book3S HV: Make idle_kvm_start_guest() return 0 if it went to guest 2021-10-16 00:40:03 +11:00
lib powerpc/lib: Add helper to check if offset is within conditional branch range 2021-10-07 18:52:33 +11:00
math-emu powerpc/64s: avoid reloading (H)SRR registers if they are still valid 2021-06-25 00:06:55 +10:00
mm Merge branch 'akpm' (patches from Andrew) 2021-09-08 12:55:35 -07:00
net powerpc/bpf ppc32: Fix BPF_SUB when imm == 0x80000000 2021-10-07 19:52:59 +11:00
perf powerpc/perf: Fix the check for SIAR value 2021-08-25 22:38:19 +10:00
platforms pseries/eeh: Fix the kdump kernel crash during eeh_pseries_init 2021-10-07 23:37:22 +11:00
purgatory powerpc/kexec: Don't use .machine ppc64 in trampoline_64.S 2021-04-08 21:17:43 +10:00
sysdev powerpc/xive: Discard disabled interrupts in get_irqchip_state() 2021-10-13 16:38:55 +11:00
tools powerpc/head_check: Fix shellcheck errors 2021-08-17 22:52:02 +10:00
xmon powerpc: Refactor verification of MSR_RI 2021-08-26 21:21:07 +10:00
Kbuild
Kconfig Tracing updates for 5.15: 2021-09-05 11:50:41 -07:00
Kconfig.debug powerpc/ptdump: Convert powerpc to GENERIC_PTDUMP 2021-08-25 13:35:48 +10:00
Makefile powerpc: Add "-z notext" flag to disable diagnostic 2021-08-15 13:49:39 +10:00
Makefile.postlink