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SubjectRe: [patch v2 ] mm/zs_malloc: Fix bit spinlock replacement
On 2016-10-19 17:50:38 [+0200], Mike Galbraith wrote:
>
> Do not alter HANDLE_SIZE, memory corruption ensues. The handle is
> a pointer, allocate space for the struct it points to and align it
> ZS_ALIGN. Also, when accessing the struct, mask HANDLE_PIN_BIT.
>
> v2: mutex is only needed for PREEMPT_RT_FULL, with PREEMPT_RT_RTB,
> preemption is disabled when we take it...
>
> Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>

The folded version:


From: Mike Galbraith <umgwanakikbuti@gmail.com>
Date: Tue, 22 Mar 2016 11:16:09 +0100
Subject: [PATCH] mm/zsmalloc: copy with get_cpu_var() and locking

get_cpu_var() disables preemption and triggers a might_sleep() splat later.
This is replaced with get_locked_var().
This bitspinlocks are replaced with a proper mutex which requires a slightly
larger struct to allocate.

Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
[bigeasy: replace the bitspin_lock() with a mutex, get_locked_var(). Mike then
fixed the size magic]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
mm/zsmalloc.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 74 insertions(+), 6 deletions(-)

--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -53,6 +53,7 @@
#include <linux/mount.h>
#include <linux/migrate.h>
#include <linux/pagemap.h>
+#include <linux/locallock.h>

#define ZSPAGE_MAGIC 0x58

@@ -70,9 +71,22 @@
*/
#define ZS_MAX_ZSPAGE_ORDER 2
#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)
-
#define ZS_HANDLE_SIZE (sizeof(unsigned long))

+#ifdef CONFIG_PREEMPT_RT_FULL
+
+struct zsmalloc_handle {
+ unsigned long addr;
+ struct mutex lock;
+};
+
+#define ZS_HANDLE_ALLOC_SIZE (sizeof(struct zsmalloc_handle))
+
+#else
+
+#define ZS_HANDLE_ALLOC_SIZE (sizeof(unsigned long))
+#endif
+
/*
* Object location (<PFN>, <obj_idx>) is encoded as
* as single (unsigned long) handle value.
@@ -327,7 +341,7 @@ static void SetZsPageMovable(struct zs_p

static int create_cache(struct zs_pool *pool)
{
- pool->handle_cachep = kmem_cache_create("zs_handle", ZS_HANDLE_SIZE,
+ pool->handle_cachep = kmem_cache_create("zs_handle", ZS_HANDLE_ALLOC_SIZE,
0, 0, NULL);
if (!pool->handle_cachep)
return 1;
@@ -351,10 +365,27 @@ static void destroy_cache(struct zs_pool

static unsigned long cache_alloc_handle(struct zs_pool *pool, gfp_t gfp)
{
- return (unsigned long)kmem_cache_alloc(pool->handle_cachep,
- gfp & ~(__GFP_HIGHMEM|__GFP_MOVABLE));
+ void *p;
+
+ p = kmem_cache_alloc(pool->handle_cachep,
+ gfp & ~(__GFP_HIGHMEM|__GFP_MOVABLE));
+#ifdef CONFIG_PREEMPT_RT_FULL
+ if (p) {
+ struct zsmalloc_handle *zh = p;
+
+ mutex_init(&zh->lock);
+ }
+#endif
+ return (unsigned long)p;
}

+#ifdef CONFIG_PREEMPT_RT_FULL
+static struct zsmalloc_handle *zs_get_pure_handle(unsigned long handle)
+{
+ return (void *)(handle &~((1 << OBJ_TAG_BITS) - 1));
+}
+#endif
+
static void cache_free_handle(struct zs_pool *pool, unsigned long handle)
{
kmem_cache_free(pool->handle_cachep, (void *)handle);
@@ -373,12 +404,18 @@ static void cache_free_zspage(struct zs_

static void record_obj(unsigned long handle, unsigned long obj)
{
+#ifdef CONFIG_PREEMPT_RT_FULL
+ struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
+
+ WRITE_ONCE(zh->addr, obj);
+#else
/*
* lsb of @obj represents handle lock while other bits
* represent object value the handle is pointing so
* updating shouldn't do store tearing.
*/
WRITE_ONCE(*(unsigned long *)handle, obj);
+#endif
}

/* zpool driver */
@@ -467,6 +504,7 @@ MODULE_ALIAS("zpool-zsmalloc");

/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
static DEFINE_PER_CPU(struct mapping_area, zs_map_area);
+static DEFINE_LOCAL_IRQ_LOCK(zs_map_area_lock);

static bool is_zspage_isolated(struct zspage *zspage)
{
@@ -902,7 +940,13 @@ static unsigned long location_to_obj(str

static unsigned long handle_to_obj(unsigned long handle)
{
+#ifdef CONFIG_PREEMPT_RT_FULL
+ struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
+
+ return zh->addr;
+#else
return *(unsigned long *)handle;
+#endif
}

static unsigned long obj_to_head(struct page *page, void *obj)
@@ -916,22 +960,46 @@ static unsigned long obj_to_head(struct

static inline int testpin_tag(unsigned long handle)
{
+#ifdef CONFIG_PREEMPT_RT_FULL
+ struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
+
+ return mutex_is_locked(&zh->lock);
+#else
return bit_spin_is_locked(HANDLE_PIN_BIT, (unsigned long *)handle);
+#endif
}

static inline int trypin_tag(unsigned long handle)
{
+#ifdef CONFIG_PREEMPT_RT_FULL
+ struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
+
+ return mutex_trylock(&zh->lock);
+#else
return bit_spin_trylock(HANDLE_PIN_BIT, (unsigned long *)handle);
+#endif
}

static void pin_tag(unsigned long handle)
{
+#ifdef CONFIG_PREEMPT_RT_FULL
+ struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
+
+ return mutex_lock(&zh->lock);
+#else
bit_spin_lock(HANDLE_PIN_BIT, (unsigned long *)handle);
+#endif
}

static void unpin_tag(unsigned long handle)
{
+#ifdef CONFIG_PREEMPT_RT_FULL
+ struct zsmalloc_handle *zh = zs_get_pure_handle(handle);
+
+ return mutex_unlock(&zh->lock);
+#else
bit_spin_unlock(HANDLE_PIN_BIT, (unsigned long *)handle);
+#endif
}

static void reset_page(struct page *page)
@@ -1423,7 +1491,7 @@ void *zs_map_object(struct zs_pool *pool
class = pool->size_class[class_idx];
off = (class->size * obj_idx) & ~PAGE_MASK;

- area = &get_cpu_var(zs_map_area);
+ area = &get_locked_var(zs_map_area_lock, zs_map_area);
area->vm_mm = mm;
if (off + class->size <= PAGE_SIZE) {
/* this object is contained entirely within a page */
@@ -1477,7 +1545,7 @@ void zs_unmap_object(struct zs_pool *poo

__zs_unmap_object(area, pages, off, class->size);
}
- put_cpu_var(zs_map_area);
+ put_locked_var(zs_map_area_lock, zs_map_area);

migrate_read_unlock(zspage);
unpin_tag(handle);
Sebastian

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