Messages in this thread Patch in this message | | | Date | Thu, 1 May 2008 14:46:28 -0400 | From | Mathieu Desnoyers <> | Subject | [PATCH] Fix SMP alternatives : use mutex instead of spinlock, text_poke is sleepable |
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* Luca Tettamanti (kronos.it@gmail.com) wrote: > On Thu, May 1, 2008 at 5:02 PM, Luca Tettamanti <kronos.it@gmail.com> wrote: > > On Thu, May 1, 2008 at 3:04 PM, Mathieu Desnoyers > > <mathieu.desnoyers@polymtl.ca> wrote: > > > * Luca Tettamanti (kronos.it@gmail.com) wrote: > > > > Hello, > > > > with git current I'm seeing these warnings when bringing CPUs down: > > > > > > > > > > > > > Hi Luca, > > > > > > Does your tree include the patch posted here ? > > > > > > http://lkml.org/lkml/2008/4/19/139 > > > > Nope, I was using vanilla kernel (smp_alt is still a spinlock). Will > > test the patch ASAP. > > Tested the patch: works fine, and the system is stable after multiple > up&down, I'm not experiencing a reboot. > > Luca
Ingo, Linus,
I guess fast-tracking pulling the following patch into mainline wouldn't hurt. I just updated it so it applies to mainline.
Thanks,
Mathieu
Fix SMP alternatives : use mutex instead of spinlock, text_poke is sleepable
* Pekka Paalanen (pq@iki.fi) wrote: > On Mon, 14 Apr 2008 08:57:13 +0200 > Ingo Molnar <mingo@elte.hu> wrote: > > > Pekka Paalanen wrote: > > > 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. > > > > there's no known bug of sched-devel/latest of this kind (or any known > > bug for that matter). > > > > i suspect the bug is that you bring the CPU down from an atomic > > (spinlocked or irq disabled) context. > > I have been eyeballing the code in current sched-devel/latest and there's > something I think I found. > > This is the beginning of my enter_uniprocessor() which is called from > enable_mmiotrace() seen in the backtrace. > > static void enter_uniprocessor(void) > { > 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); > > The function get_online_cpus() calls might_sleep(), so at that > point everything is fine. > > Following the backtrace, we come to alternatives_smp_switch(), > which does > spin_lock(&smp_alt); > and then continues eventually into this function: > > void *__kprobes text_poke(void *addr, const void *opcode, size_t len) > { > unsigned long flags; > char *vaddr; > int nr_pages = 2; > > BUG_ON(len > sizeof(long)); > BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1)) > - ((long)addr & ~(sizeof(long) - 1))); > if (kernel_text_address((unsigned long)addr)) { > struct page *pages[2] = { virt_to_page(addr), > virt_to_page(addr + PAGE_SIZE) }; > if (!pages[1]) > nr_pages = 1; > vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL); > > After which we find ourselves in > > struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags, > unsigned long start, unsigned long end) > { > return __get_vm_area_node(size, flags, start, end, -1, GFP_KERNEL); > > and in __get_vm_area_node() there is > area = kmalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node); > > where gfp_mask is now GFP_KERNEL. As far as I can tell, using SLAB, > kmalloc_node() here is actually kmalloc(). Anyway, looks like we end up > in __kmalloc with such flags that it may sleep. > > I have followed the code so that the path up to kmalloc_node() is > possible, unless there are some "should never happen" conditions > along the way, which I just cannot know of. > > Is this the bug? >
Yep. I think using a mutex should fix it. There is no reason to use a spinlock rather than a mutex here.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> CC: Pekka Paalanen <pq@iki.fi> CC: Ingo Molnar <mingo@elte.hu> CC: Steven Rostedt <rostedt@goodmis.org> --- arch/x86/kernel/alternative.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-)
Index: linux-2.6-lttng/arch/x86/kernel/alternative.c =================================================================== --- linux-2.6-lttng.orig/arch/x86/kernel/alternative.c 2008-05-01 14:41:09.000000000 -0400 +++ linux-2.6-lttng/arch/x86/kernel/alternative.c 2008-05-01 14:44:28.000000000 -0400 @@ -1,6 +1,6 @@ #include <linux/module.h> #include <linux/sched.h> -#include <linux/spinlock.h> +#include <linux/mutex.h> #include <linux/list.h> #include <linux/kprobes.h> #include <linux/mm.h> @@ -279,7 +279,7 @@ struct smp_alt_module { struct list_head next; }; static LIST_HEAD(smp_alt_modules); -static DEFINE_SPINLOCK(smp_alt); +static DEFINE_MUTEX(smp_alt); static int smp_mode = 1; /* protected by smp_alt */ void alternatives_smp_module_add(struct module *mod, char *name, @@ -312,12 +312,12 @@ void alternatives_smp_module_add(struct __func__, smp->locks, smp->locks_end, smp->text, smp->text_end, smp->name); - spin_lock(&smp_alt); + mutex_lock(&smp_alt); list_add_tail(&smp->next, &smp_alt_modules); if (boot_cpu_has(X86_FEATURE_UP)) alternatives_smp_unlock(smp->locks, smp->locks_end, smp->text, smp->text_end); - spin_unlock(&smp_alt); + mutex_unlock(&smp_alt); } void alternatives_smp_module_del(struct module *mod) @@ -327,17 +327,17 @@ void alternatives_smp_module_del(struct if (smp_alt_once || noreplace_smp) return; - spin_lock(&smp_alt); + mutex_lock(&smp_alt); list_for_each_entry(item, &smp_alt_modules, next) { if (mod != item->mod) continue; list_del(&item->next); - spin_unlock(&smp_alt); + mutex_unlock(&smp_alt); DPRINTK("%s: %s\n", __func__, item->name); kfree(item); return; } - spin_unlock(&smp_alt); + mutex_unlock(&smp_alt); } void alternatives_smp_switch(int smp) @@ -359,7 +359,7 @@ void alternatives_smp_switch(int smp) return; BUG_ON(!smp && (num_online_cpus() > 1)); - spin_lock(&smp_alt); + mutex_lock(&smp_alt); /* * Avoid unnecessary switches because it forces JIT based VMs to @@ -383,7 +383,7 @@ void alternatives_smp_switch(int smp) mod->text, mod->text_end); } smp_mode = smp; - spin_unlock(&smp_alt); + mutex_unlock(&smp_alt); } #endif -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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