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Message-Id: <1185208378.8197.20.camel@twins>
Date: Mon, 23 Jul 2007 18:32:58 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Daniel Walker <dwalker@...sta.com>
Cc: mingo@...e.hu, paulmck@...ux.vnet.ibm.com,
linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH] release quicklist before free_page
On Mon, 2007-07-23 at 08:21 -0700, Daniel Walker wrote:
> Resolves,
>
> BUG: sleeping function called from invalid context cc1(29651) at kernel/rtmutex.c:636
> in_atomic():1 [00000001], irqs_disabled():0
> [<c0119f50>] __might_sleep+0xf3/0xf9
> [<c031600e>] __rt_spin_lock+0x21/0x3c
> [<c014102c>] get_zone_pcp+0x20/0x29
> [<c0141a40>] free_hot_cold_page+0xdc/0x167
> [<c013a3f4>] add_preempt_count+0x12/0xcc
> [<c0110d92>] pgd_dtor+0x0/0x1
> [<c015d865>] quicklist_trim+0xb7/0xe3
> [<c0111025>] check_pgt_cache+0x19/0x1c
> [<c0148df5>] free_pgtables+0x54/0x12c
> [<c013a3f4>] add_preempt_count+0x12/0xcc
> [<c014e5be>] unmap_region+0xeb/0x13b
>
>
> It looks like the quicklist isn't used after a few variables are evaluated.
> So no need to keep preemption disabled over the whole function.
Not quite, it uses preempt_disable() to avoid migration and stick to a
cpu. Without that it might end up freeing pages from another quicklist.
How about this - compile tested only
---
We cannot call the page allocator with preemption-disabled, use the
per_cpu_locked construct to allow preemption while guarding the per cpu
data.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
include/linux/quicklist.h | 19 +++++++++++++++----
mm/quicklist.c | 9 +++++----
2 files changed, 20 insertions(+), 8 deletions(-)
Index: linux-2.6/include/linux/quicklist.h
===================================================================
--- linux-2.6.orig/include/linux/quicklist.h
+++ linux-2.6/include/linux/quicklist.h
@@ -18,7 +18,7 @@ struct quicklist {
int nr_pages;
};
-DECLARE_PER_CPU(struct quicklist, quicklist)[CONFIG_NR_QUICK];
+DECLARE_PER_CPU_LOCKED(struct quicklist, quicklist)[CONFIG_NR_QUICK];
/*
* The two key functions quicklist_alloc and quicklist_free are inline so
@@ -30,19 +30,30 @@ DECLARE_PER_CPU(struct quicklist, quickl
* The fast patch in quicklist_alloc touched only a per cpu cacheline and
* the first cacheline of the page itself. There is minmal overhead involved.
*/
-static inline void *quicklist_alloc(int nr, gfp_t flags, void (*ctor)(void *))
+static inline void *__quicklist_alloc(int cpu, int nr, gfp_t flags, void (*ctor)(void *))
{
struct quicklist *q;
void **p = NULL;
- q =&get_cpu_var(quicklist)[nr];
+ q = &__get_cpu_var_locked(quicklist, cpu)[nr];
p = q->page;
if (likely(p)) {
q->page = p[0];
p[0] = NULL;
q->nr_pages--;
}
- put_cpu_var(quicklist);
+ return p;
+}
+
+static inline void *quicklist_alloc(int nr, gfp_t flags, void (*ctor)(void *))
+{
+ struct quicklist *q;
+ void **p = NULL;
+ int cpu;
+
+ (void)get_cpu_var_locked(quicklist, &cpu)[nr];
+ p = __quicklist_alloc(cpu, nr, flags, ctor);
+ put_cpu_var_locked(quicklist, cpu);
if (likely(p))
return p;
Index: linux-2.6/mm/quicklist.c
===================================================================
--- linux-2.6.orig/mm/quicklist.c
+++ linux-2.6/mm/quicklist.c
@@ -19,7 +19,7 @@
#include <linux/module.h>
#include <linux/quicklist.h>
-DEFINE_PER_CPU(struct quicklist, quicklist)[CONFIG_NR_QUICK];
+DEFINE_PER_CPU_LOCKED(struct quicklist, quicklist)[CONFIG_NR_QUICK];
#define FRACTION_OF_NODE_MEM 16
@@ -51,8 +51,9 @@ void quicklist_trim(int nr, void (*dtor)
{
long pages_to_free;
struct quicklist *q;
+ int cpu;
- q = &get_cpu_var(quicklist)[nr];
+ q = &get_cpu_var_locked(quicklist, &cpu)[nr];
if (q->nr_pages > min_pages) {
pages_to_free = min_pages_to_free(q, min_pages, max_free);
@@ -61,7 +62,7 @@ void quicklist_trim(int nr, void (*dtor)
* We pass a gfp_t of 0 to quicklist_alloc here
* because we will never call into the page allocator.
*/
- void *p = quicklist_alloc(nr, 0, NULL);
+ void *p = __quicklist_alloc(cpu, nr, 0, NULL);
if (dtor)
dtor(p);
@@ -69,7 +70,7 @@ void quicklist_trim(int nr, void (*dtor)
pages_to_free--;
}
}
- put_cpu_var(quicklist);
+ put_cpu_var_locked(quicklist, cpu);
}
unsigned long quicklist_total_size(void)
-
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