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
1 parent 496c5fe
asequencer.h
/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Main header file for the ALSA sequencer
* Copyright (c) 1998-1999 by Frank van de Pol <fvdpol@coil.demon.nl>
* (c) 1998-1999 by Jaroslav Kysela <perex@perex.cz>
*/
#ifndef __SOUND_ASEQUENCER_H
#define __SOUND_ASEQUENCER_H
#include <linux/ioctl.h>
#include <sound/asound.h>
#include <uapi/sound/asequencer.h>
/* helper macro */
#define snd_seq_event_bounce_ext_data(ev) ((void*)((char *)(ev)->data.ext.ptr + sizeof(struct snd_seq_event_bounce)))
/*
* type check macros
*/
/* result events: 0-4 */
#define snd_seq_ev_is_result_type(ev) ((ev)->type < 5)
/* channel specific events: 5-19 */
#define snd_seq_ev_is_channel_type(ev) ((ev)->type >= 5 && (ev)->type < 20)
/* note events: 5-9 */
#define snd_seq_ev_is_note_type(ev) ((ev)->type >= 5 && (ev)->type < 10)
/* control events: 10-19 */
#define snd_seq_ev_is_control_type(ev) ((ev)->type >= 10 && (ev)->type < 20)
/* queue control events: 30-39 */
#define snd_seq_ev_is_queue_type(ev) ((ev)->type >= 30 && (ev)->type < 40)
/* system status messages */
#define snd_seq_ev_is_message_type(ev) ((ev)->type >= 60 && (ev)->type < 69)
/* sample messages */
#define snd_seq_ev_is_sample_type(ev) ((ev)->type >= 70 && (ev)->type < 79)
/* user-defined messages */
#define snd_seq_ev_is_user_type(ev) ((ev)->type >= 90 && (ev)->type < 99)
/* fixed length events: 0-99 */
#define snd_seq_ev_is_fixed_type(ev) ((ev)->type < 100)
/* variable length events: 130-139 */
#define snd_seq_ev_is_variable_type(ev) ((ev)->type >= 130 && (ev)->type < 140)
/* reserved for kernel */
#define snd_seq_ev_is_reserved(ev) ((ev)->type >= 150)
/* direct dispatched events */
#define snd_seq_ev_is_direct(ev) ((ev)->queue == SNDRV_SEQ_QUEUE_DIRECT)
/*
* macros to check event flags
*/
/* prior events */
#define snd_seq_ev_is_prior(ev) (((ev)->flags & SNDRV_SEQ_PRIORITY_MASK) == SNDRV_SEQ_PRIORITY_HIGH)
/* event length type */
#define snd_seq_ev_length_type(ev) ((ev)->flags & SNDRV_SEQ_EVENT_LENGTH_MASK)
#define snd_seq_ev_is_fixed(ev) (snd_seq_ev_length_type(ev) == SNDRV_SEQ_EVENT_LENGTH_FIXED)
#define snd_seq_ev_is_variable(ev) (snd_seq_ev_length_type(ev) == SNDRV_SEQ_EVENT_LENGTH_VARIABLE)
#define snd_seq_ev_is_varusr(ev) (snd_seq_ev_length_type(ev) == SNDRV_SEQ_EVENT_LENGTH_VARUSR)
/* time-stamp type */
#define snd_seq_ev_timestamp_type(ev) ((ev)->flags & SNDRV_SEQ_TIME_STAMP_MASK)
#define snd_seq_ev_is_tick(ev) (snd_seq_ev_timestamp_type(ev) == SNDRV_SEQ_TIME_STAMP_TICK)
#define snd_seq_ev_is_real(ev) (snd_seq_ev_timestamp_type(ev) == SNDRV_SEQ_TIME_STAMP_REAL)
/* time-mode type */
#define snd_seq_ev_timemode_type(ev) ((ev)->flags & SNDRV_SEQ_TIME_MODE_MASK)
#define snd_seq_ev_is_abstime(ev) (snd_seq_ev_timemode_type(ev) == SNDRV_SEQ_TIME_MODE_ABS)
#define snd_seq_ev_is_reltime(ev) (snd_seq_ev_timemode_type(ev) == SNDRV_SEQ_TIME_MODE_REL)
/* queue sync port */
#define snd_seq_queue_sync_port(q) ((q) + 16)
#endif /* __SOUND_ASEQUENCER_H */
Computing file changes ...
