(mem hotplug, pcpu_alloc) BUG: sleeping function called from invalid context at kernel/mutex.c:94

(mem hotplug, pcpu_alloc) BUG: sleeping function called from invalid context at kernel/mutex.c:94

[Alok Kataria]

Hi,

We have seen following might_sleep warning while hot adding memory...

[  142.339267] BUG: sleeping function called from invalid context at kernel/mutex.c:94
[  142.339276] in_atomic(): 0, irqs_disabled(): 1, pid: 4, name: migration/0
[  142.339283] Pid: 4, comm: migration/0 Not tainted 2.6.35.6-45.fc14.x86_64 #1
[  142.339288] Call Trace:
[  142.339305]  [<ffffffff8103d12b>] __might_sleep+0xeb/0xf0
[  142.339316]  [<ffffffff81468245>] mutex_lock+0x24/0x50
[  142.339326]  [<ffffffff8110eaa6>] pcpu_alloc+0x6d/0x7ee
[  142.339336]  [<ffffffff81048888>] ? load_balance+0xbe/0x60e
[  142.339343]  [<ffffffff8103a1b3>] ? rt_se_boosted+0x21/0x2f
[  142.339349]  [<ffffffff8103e1cf>] ? dequeue_rt_stack+0x18b/0x1ed
[  142.339356]  [<ffffffff8110f237>] __alloc_percpu+0x10/0x12
[  142.339362]  [<ffffffff81465e22>] setup_zone_pageset+0x38/0xbe
[  142.339373]  [<ffffffff810d6d81>] ? build_zonelists_node.clone.58+0x79/0x8c
[  142.339384]  [<ffffffff81452539>] __build_all_zonelists+0x419/0x46c
[  142.339395]  [<ffffffff8108ef01>] ? cpu_stopper_thread+0xb2/0x198
[  142.339401]  [<ffffffff8108f075>] stop_machine_cpu_stop+0x8e/0xc5
[  142.339407]  [<ffffffff8108efe7>] ? stop_machine_cpu_stop+0x0/0xc5
[  142.339414]  [<ffffffff8108ef57>] cpu_stopper_thread+0x108/0x198
[  142.339420]  [<ffffffff81467a37>] ? schedule+0x5b2/0x5cc
[  142.339426]  [<ffffffff8108ee4f>] ? cpu_stopper_thread+0x0/0x198
[  142.339434]  [<ffffffff81065f29>] kthread+0x7f/0x87
[  142.339443]  [<ffffffff8100aae4>] kernel_thread_helper+0x4/0x10
[  142.339449]  [<ffffffff81065eaa>] ? kthread+0x0/0x87
[  142.339455]  [<ffffffff8100aae0>] ? kernel_thread_helper+0x0/0x10
[  142.340099] Built 5 zonelists in Node order, mobility grouping on.  Total pages: 289456
[  142.340108] Policy zone: Normal


This warning was seen on the FC14 kernel, though looking at the current
git, the problem seems to exist on mainline too.
The problem is that pcpu_alloc expects that it is called from non-atomic
context as a result it grabs the pcpu_alloc_mutex. 
In the memory-hotplug case though, we do end up calling pcpu_alloc from
atomic context, while all cpus are stopped.

void build_all_zonelists(void *data)
{
   set_zonelist_order();

   if (system_state == SYSTEM_BOOTING) {
      __build_all_zonelists(NULL);
      mminit_verify_zonelist();
      cpuset_init_current_mems_allowed();
   } else {
      /* we have to stop all cpus to guarantee there is no user
         of zonelist */
      stop_machine(__build_all_zonelists, data, NULL);   <=========
      /* cpuset refresh routine should be here */
   }

__build_all_zonelists eventually calls pcpu_alloc. 

I didn't dive through the history, so am not sure when was this
regression introduced, but could have regressed with the new pcpu memory
allocator.

--
Alok

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Re: (mem hotplug, pcpu_alloc) BUG: sleeping function called from invalid context at kernel/mutex.c:94

[Tejun Heo]

Hello,

On 11/12/2010 07:56 PM, Alok Kataria wrote:
> We have seen following might_sleep warning while hot adding memory...
> 
> [  142.339267] BUG: sleeping function called from invalid context at kernel/mutex.c:94
> [  142.339276] in_atomic(): 0, irqs_disabled(): 1, pid: 4, name: migration/0
> [  142.339283] Pid: 4, comm: migration/0 Not tainted 2.6.35.6-45.fc14.x86_64 #1
> [  142.339288] Call Trace:
> [  142.339305]  [<ffffffff8103d12b>] __might_sleep+0xeb/0xf0
> [  142.339316]  [<ffffffff81468245>] mutex_lock+0x24/0x50
> [  142.339326]  [<ffffffff8110eaa6>] pcpu_alloc+0x6d/0x7ee
> [  142.339336]  [<ffffffff81048888>] ? load_balance+0xbe/0x60e
> [  142.339343]  [<ffffffff8103a1b3>] ? rt_se_boosted+0x21/0x2f
> [  142.339349]  [<ffffffff8103e1cf>] ? dequeue_rt_stack+0x18b/0x1ed
> [  142.339356]  [<ffffffff8110f237>] __alloc_percpu+0x10/0x12
> [  142.339362]  [<ffffffff81465e22>] setup_zone_pageset+0x38/0xbe
> [  142.339373]  [<ffffffff810d6d81>] ? build_zonelists_node.clone.58+0x79/0x8c
> [  142.339384]  [<ffffffff81452539>] __build_all_zonelists+0x419/0x46c
> [  142.339395]  [<ffffffff8108ef01>] ? cpu_stopper_thread+0xb2/0x198
> [  142.339401]  [<ffffffff8108f075>] stop_machine_cpu_stop+0x8e/0xc5
> [  142.339407]  [<ffffffff8108efe7>] ? stop_machine_cpu_stop+0x0/0xc5
> [  142.339414]  [<ffffffff8108ef57>] cpu_stopper_thread+0x108/0x198
> [  142.339420]  [<ffffffff81467a37>] ? schedule+0x5b2/0x5cc
> [  142.339426]  [<ffffffff8108ee4f>] ? cpu_stopper_thread+0x0/0x198
> [  142.339434]  [<ffffffff81065f29>] kthread+0x7f/0x87
> [  142.339443]  [<ffffffff8100aae4>] kernel_thread_helper+0x4/0x10
> [  142.339449]  [<ffffffff81065eaa>] ? kthread+0x0/0x87
> [  142.339455]  [<ffffffff8100aae0>] ? kernel_thread_helper+0x0/0x10
> [  142.340099] Built 5 zonelists in Node order, mobility grouping on.  Total pages: 289456
> [  142.340108] Policy zone: Normal
> 
> 
> This warning was seen on the FC14 kernel, though looking at the current
> git, the problem seems to exist on mainline too.
> The problem is that pcpu_alloc expects that it is called from non-atomic
> context as a result it grabs the pcpu_alloc_mutex. 
> In the memory-hotplug case though, we do end up calling pcpu_alloc from
> atomic context, while all cpus are stopped.
> 
> void build_all_zonelists(void *data)
> {
>    set_zonelist_order();
> 
>    if (system_state == SYSTEM_BOOTING) {
>       __build_all_zonelists(NULL);
>       mminit_verify_zonelist();
>       cpuset_init_current_mems_allowed();
>    } else {
>       /* we have to stop all cpus to guarantee there is no user
>          of zonelist */
>       stop_machine(__build_all_zonelists, data, NULL);   <=========
>       /* cpuset refresh routine should be here */
>    }
> 
> __build_all_zonelists eventually calls pcpu_alloc. 
> 
> I didn't dive through the history, so am not sure when was this
> regression introduced, but could have regressed with the new pcpu memory
> allocator.

Meh... the percpu allocator required user context from the beginning.
The new allocator didn't change that.

Wouldn't it be possible to prepare hotplug outside of cpu_stop and use
stop_machine() only to make it available to the system.  In general,
it's a very bad idea to allocate memory from inside stop_machine.  The
whole machine is stopped, after all.  In general, it shouldn't be too
difficult to add new resource without stop_machine too unlike removing
one.  Pekka, Christoph, any ideas?

Thanks.

-- 
tejun

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[BUGFIX][PATCH] fix build_all_zonelist where percpu_alloc is wrongly called under stop_machine_run (Was Re: (mem hotplug, pcpu_alloc) BUG: sleeping function called from invalid context at kernel/mutex.c:94

[KAMEZAWA Hiroyuki]

On Sat, 13 Nov 2010 11:09:23 +0100
Tejun Heo <tj@kernel.org> wrote:

> Meh... the percpu allocator required user context from the beginning.
> The new allocator didn't change that.
> 
> Wouldn't it be possible to prepare hotplug outside of cpu_stop and use
> stop_machine() only to make it available to the system.  In general,
> it's a very bad idea to allocate memory from inside stop_machine.  The
> whole machine is stopped, after all.  In general, it shouldn't be too
> difficult to add new resource without stop_machine too unlike removing
> one.  Pekka, Christoph, any ideas?
> 

Fix here. I'm glad if someone test this.
==

At memory hotplug, build_allzonelists() may be called under stop_machine_run().
In this function, setup_zone_pageset() is called. But it's bug because it
will do page allocation under stop_machine_run().

Here is a report from Alok Kataria.

[  142.339267] BUG: sleeping function called from invalid context at kernel/mutex.c:94
[  142.339276] in_atomic(): 0, irqs_disabled(): 1, pid: 4, name: migration/0
[  142.339283] Pid: 4, comm: migration/0 Not tainted 2.6.35.6-45.fc14.x86_64 #1
[  142.339288] Call Trace:
[  142.339305]  [<ffffffff8103d12b>] __might_sleep+0xeb/0xf0
[  142.339316]  [<ffffffff81468245>] mutex_lock+0x24/0x50
[  142.339326]  [<ffffffff8110eaa6>] pcpu_alloc+0x6d/0x7ee
[  142.339336]  [<ffffffff81048888>] ? load_balance+0xbe/0x60e
[  142.339343]  [<ffffffff8103a1b3>] ? rt_se_boosted+0x21/0x2f
[  142.339349]  [<ffffffff8103e1cf>] ? dequeue_rt_stack+0x18b/0x1ed
[  142.339356]  [<ffffffff8110f237>] __alloc_percpu+0x10/0x12
[  142.339362]  [<ffffffff81465e22>] setup_zone_pageset+0x38/0xbe
[  142.339373]  [<ffffffff810d6d81>] ? build_zonelists_node.clone.58+0x79/0x8c
[  142.339384]  [<ffffffff81452539>] __build_all_zonelists+0x419/0x46c
[  142.339395]  [<ffffffff8108ef01>] ? cpu_stopper_thread+0xb2/0x198
[  142.339401]  [<ffffffff8108f075>] stop_machine_cpu_stop+0x8e/0xc5
[  142.339407]  [<ffffffff8108efe7>] ? stop_machine_cpu_stop+0x0/0xc5
[  142.339414]  [<ffffffff8108ef57>] cpu_stopper_thread+0x108/0x198
[  142.339420]  [<ffffffff81467a37>] ? schedule+0x5b2/0x5cc
[  142.339426]  [<ffffffff8108ee4f>] ? cpu_stopper_thread+0x0/0x198
[  142.339434]  [<ffffffff81065f29>] kthread+0x7f/0x87
[  142.339443]  [<ffffffff8100aae4>] kernel_thread_helper+0x4/0x10
[  142.339449]  [<ffffffff81065eaa>] ? kthread+0x0/0x87
[  142.339455]  [<ffffffff8100aae0>] ? kernel_thread_helper+0x0/0x10
[  142.340099] Built 5 zonelists in Node order, mobility grouping on.  Total pages: 289456
[  142.340108] Policy zone: Normal

This patch tries to fix the issue by moving setup_zone_pageset() out from
stop_machine_run(). It's obviously not necessary to be called under
stop_machine_run().

Reported-by: Alok Kataria <akataria@vmware.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/page_alloc.c |   16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

Index: mmotm-1117/mm/page_alloc.c
===================================================================
--- mmotm-1117.orig/mm/page_alloc.c
+++ mmotm-1117/mm/page_alloc.c
@@ -3027,14 +3027,6 @@ static __init_refok int __build_all_zone
 		build_zonelist_cache(pgdat);
 	}
 
-#ifdef CONFIG_MEMORY_HOTPLUG
-	/* Setup real pagesets for the new zone */
-	if (data) {
-		struct zone *zone = data;
-		setup_zone_pageset(zone);
-	}
-#endif
-
 	/*
 	 * Initialize the boot_pagesets that are going to be used
 	 * for bootstrapping processors. The real pagesets for
@@ -3083,7 +3075,13 @@ void build_all_zonelists(void *data)
 	} else {
 		/* we have to stop all cpus to guarantee there is no user
 		   of zonelist */
-		stop_machine(__build_all_zonelists, data, NULL);
+#ifdef CONFIG_MEMORY_HOTPLUG
+		if (data) {
+			struct zone *zone = (struct zone *)data;
+			setup_zone_pageset(zone);
+		}
+#endif
+		stop_machine(__build_all_zonelists, NULL, NULL);
 		/* cpuset refresh routine should be here */
 	}
 	vm_total_pages = nr_free_pagecache_pages();

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