Messages in this thread Patch in this message | | | Date | Sun, 13 Apr 2008 23:05:52 +0300 | From | Pekka Paalanen <> | Subject | [BUG/PATCH] x86 mmiotrace: dynamically disable non-boot CPUs |
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From 9d00d006631650e8ba9131356c544a5ae79f873e Mon Sep 17 00:00:00 2001 From: Pekka Paalanen <pq@iki.fi> Date: Sat, 12 Apr 2008 00:18:57 +0300 Subject: [PATCH] x86 mmiotrace: dynamically disable non-boot CPUs
Mmiotrace is not reliable with multiple CPUs and may miss events. Drop to single CPU when mmiotrace is activated.
Signed-off-by: Pekka Paalanen <pq@iki.fi> ---
When I tested this patch on Intel Core 2 Duo, enter_uniprocessor() triggered the following kernel bug:
Linux version 2.6.25-rc8-sched-devel.git-x86-latest.git (paalanen@ct200006) (gcc version 4.1.2 (Gentoo 4.1.2 p1.0.1)) #2 SMP PREEMPT Sun Apr 13 22:09:03 EEST 2008 ... in mmio_trace_init mmiotrace: Disabling non-boot CPUs... CPU 1 is now offline lockdep: fixing up alternatives. SMP alternatives: switching to UP code BUG: sleeping function called from invalid context at mm/slab.c:3053 in_atomic():1, irqs_disabled():0 5 locks held by bash/4423: #0: (trace_types_lock){--..}, at: [<ffffffff8026442f>] tracing_set_trace_write+0x93/0x11a #1: (mmiotrace_mutex){--..}, at: [<ffffffff802251e0>] enable_mmiotrace+0x17/0x142 #2: (cpu_add_remove_lock){--..}, at: [<ffffffff802580e5>] cpu_maps_update_begin+0x12/0x14 #3: (&cpu_hotplug.lock){--..}, at: [<ffffffff8025814f>] cpu_hotplug_begin+0x39/0x9f #4: (smp_alt){--..}, at: [<ffffffff80211bd9>] alternatives_smp_switch+0x66/0x1ab Pid: 4423, comm: bash Not tainted 2.6.25-rc8-sched-devel.git-x86-latest.git #2
Call Trace: [<ffffffff802520c0>] ? __debug_show_held_locks+0x22/0x24 [<ffffffff8022d292>] __might_sleep+0xd9/0xdb [<ffffffff80287326>] cache_alloc_debugcheck_before+0x23/0x32 [<ffffffff80287a32>] __kmalloc+0x34/0xa5 [<ffffffff80209393>] ? clear_ti_thread_flag+0x10/0x17 [<ffffffff8027d7f6>] kmalloc_node+0x9/0xb [<ffffffff8027d8e0>] __get_vm_area_node+0xa2/0x1cb [<ffffffff80209393>] ? clear_ti_thread_flag+0x10/0x17 [<ffffffff8027da41>] __get_vm_area+0x13/0x15 [<ffffffff8027da60>] get_vm_area+0x1d/0x1f [<ffffffff8027e14c>] vmap+0x2a/0x5c [<ffffffff8021191b>] text_poke+0xaa/0x136 [<ffffffff804cba2b>] ? _etext+0x0/0x5 [<ffffffff802119f6>] alternatives_smp_unlock+0x4f/0x63 [<ffffffff80211ce1>] alternatives_smp_switch+0x16e/0x1ab [<ffffffff8021b163>] __cpu_die+0x53/0x7d [<ffffffff802583e2>] _cpu_down+0x195/0x26c [<ffffffff802585ca>] cpu_down+0x26/0x36 [<ffffffff80225270>] enable_mmiotrace+0xa7/0x142 [<ffffffff80266b8d>] mmio_trace_init+0x3c/0x40 [<ffffffff8026448e>] tracing_set_trace_write+0xf2/0x11a [<ffffffff80327fac>] ? security_file_permission+0x11/0x13 [<ffffffff8028b047>] vfs_write+0xa7/0xe1 [<ffffffff8028b13b>] sys_write+0x47/0x6d [<ffffffff8020b4db>] system_call_after_swapgs+0x7b/0x80
mmiotrace: CPU1 is down. mmiotrace: enabled.
Is this my fault, or is there a bug somewhere else? The kernel tree is sched-devel/latest git from 12th April, IIRC.
arch/x86/mm/mmio-mod.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 51 insertions(+), 0 deletions(-)
diff --git a/arch/x86/mm/mmio-mod.c b/arch/x86/mm/mmio-mod.c index ab2bb77..f523c5f 100644 --- a/arch/x86/mm/mmio-mod.c +++ b/arch/x86/mm/mmio-mod.c @@ -32,6 +32,7 @@ #include <asm/e820.h> /* for ISA_START_ADDRESS */ #include <asm/atomic.h> #include <linux/percpu.h> +#include <linux/cpu.h> #include "pf_in.h" @@ -399,6 +400,54 @@ static void clear_trace_list(void) } } +static cpumask_t downed_cpus; + +static void enter_uniprocessor(void) +{ +#ifdef CONFIG_SMP + int cpu; + int err; + + get_online_cpus(); + downed_cpus = cpu_online_map; + cpu_clear(first_cpu(cpu_online_map), downed_cpus); + if (num_online_cpus() > 1) + pr_notice(NAME "Disabling non-boot CPUs...\n"); + put_online_cpus(); + + for_each_cpu_mask(cpu, downed_cpus) { + err = cpu_down(cpu); + if (!err) { + pr_info(NAME "CPU%d is down.\n", cpu); + } else { + pr_err(NAME "Error taking CPU%d down: %d\n", cpu, err); + } + } + if (num_online_cpus() > 1) + pr_warning(NAME "multiple CPUs still online, " + "may miss events.\n"); +#endif /* CONFIG_SMP */ +} + +static void leave_uniprocessor(void) +{ +#ifdef CONFIG_SMP + int cpu; + int err; + + if (cpus_weight(downed_cpus) == 0) + return; + pr_notice(NAME "Re-enabling CPUs...\n"); + for_each_cpu_mask(cpu, downed_cpus) { + err = cpu_up(cpu); + if (!err) + pr_info(NAME "enabled CPU%d.\n", cpu); + else + pr_err(NAME "cannot re-enable CPU%d: %d\n", cpu, err); + } +#endif /* CONFIG_SMP */ +} + #if 0 /* XXX: out of order */ static struct file_operations fops_marker = { .owner = THIS_MODULE, @@ -421,6 +470,7 @@ void enable_mmiotrace(void) if (nommiotrace) pr_info(NAME "MMIO tracing disabled.\n"); + enter_uniprocessor(); spin_lock_irq(&trace_lock); atomic_inc(&mmiotrace_enabled); spin_unlock_irq(&trace_lock); @@ -441,6 +491,7 @@ void disable_mmiotrace(void) spin_unlock_irq(&trace_lock); clear_trace_list(); /* guarantees: no more kmmio callbacks */ + leave_uniprocessor(); if (marker_file) { debugfs_remove(marker_file); marker_file = NULL; -- 1.5.3.7
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