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authorJoonsoo Kim <iamjoonsoo.kim@lge.com>2014-06-23 13:22:06 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-06-26 15:17:37 -0400
commite74eb9412b385d8cfec8966fbfd9acc871f18608 (patch)
tree90be1d0a9e5fae6be64283d4a23503b5fd09c972
parent264b86651c0986b4cf3b1e3ff48449d7afbaf0d5 (diff)
slab: fix oops when reading /proc/slab_allocators
commit 03787301420376ae41fbaf4267f4a6253d152ac5 upstream. Commit b1cb0982bdd6 ("change the management method of free objects of the slab") introduced a bug on slab leak detector ('/proc/slab_allocators'). This detector works like as following decription. 1. traverse all objects on all the slabs. 2. determine whether it is active or not. 3. if active, print who allocate this object. but that commit changed the way how to manage free objects, so the logic determining whether it is active or not is also changed. In before, we regard object in cpu caches as inactive one, but, with this commit, we mistakenly regard object in cpu caches as active one. This intoduces kernel oops if DEBUG_PAGEALLOC is enabled. If DEBUG_PAGEALLOC is enabled, kernel_map_pages() is used to detect who corrupt free memory in the slab. It unmaps page table mapping if object is free and map it if object is active. When slab leak detector check object in cpu caches, it mistakenly think this object active so try to access object memory to retrieve caller of allocation. At this point, page table mapping to this object doesn't exist, so oops occurs. Following is oops message reported from Dave. It blew up when something tried to read /proc/slab_allocators (Just cat it, and you should see the oops below) Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC Modules linked in: [snip...] CPU: 1 PID: 9386 Comm: trinity-c33 Not tainted 3.14.0-rc5+ #131 task: ffff8801aa46e890 ti: ffff880076924000 task.ti: ffff880076924000 RIP: 0010:[<ffffffffaa1a8f4a>] [<ffffffffaa1a8f4a>] handle_slab+0x8a/0x180 RSP: 0018:ffff880076925de0 EFLAGS: 00010002 RAX: 0000000000001000 RBX: 0000000000000000 RCX: 000000005ce85ce7 RDX: ffffea00079be100 RSI: 0000000000001000 RDI: ffff880107458000 RBP: ffff880076925e18 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 000000000000000f R12: ffff8801e6f84000 R13: ffffea00079be100 R14: ffff880107458000 R15: ffff88022bb8d2c0 FS: 00007fb769e45740(0000) GS:ffff88024d040000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff8801e6f84ff8 CR3: 00000000a22db000 CR4: 00000000001407e0 DR0: 0000000002695000 DR1: 0000000002695000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000070602 Call Trace: leaks_show+0xce/0x240 seq_read+0x28e/0x490 proc_reg_read+0x3d/0x80 vfs_read+0x9b/0x160 SyS_read+0x58/0xb0 tracesys+0xd4/0xd9 Code: f5 00 00 00 0f 1f 44 00 00 48 63 c8 44 3b 0c 8a 0f 84 e3 00 00 00 83 c0 01 44 39 c0 72 eb 41 f6 47 1a 01 0f 84 e9 00 00 00 89 f0 <4d> 8b 4c 04 f8 4d 85 c9 0f 84 88 00 00 00 49 8b 7e 08 4d 8d 46 RIP handle_slab+0x8a/0x180 To fix the problem, I introduce an object status buffer on each slab. With this, we can track object status precisely, so slab leak detector would not access active object and no kernel oops would occur. Memory overhead caused by this fix is only imposed to CONFIG_DEBUG_SLAB_LEAK which is mainly used for debugging, so memory overhead isn't big problem. Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> Reported-by: Dave Jones <davej@redhat.com> Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Reviewed-by: Vladimir Davydov <vdavydov@parallels.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--mm/slab.c90
1 files changed, 71 insertions, 19 deletions
diff --git a/mm/slab.c b/mm/slab.c
index 19d92181ce24..9432556ab912 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -386,6 +386,39 @@ static void **dbg_userword(struct kmem_cache *cachep, void *objp)
#endif
+#define OBJECT_FREE (0)
+#define OBJECT_ACTIVE (1)
+
+#ifdef CONFIG_DEBUG_SLAB_LEAK
+
+static void set_obj_status(struct page *page, int idx, int val)
+{
+ int freelist_size;
+ char *status;
+ struct kmem_cache *cachep = page->slab_cache;
+
+ freelist_size = cachep->num * sizeof(freelist_idx_t);
+ status = (char *)page->freelist + freelist_size;
+ status[idx] = val;
+}
+
+static inline unsigned int get_obj_status(struct page *page, int idx)
+{
+ int freelist_size;
+ char *status;
+ struct kmem_cache *cachep = page->slab_cache;
+
+ freelist_size = cachep->num * sizeof(freelist_idx_t);
+ status = (char *)page->freelist + freelist_size;
+
+ return status[idx];
+}
+
+#else
+static inline void set_obj_status(struct page *page, int idx, int val) {}
+
+#endif
+
/*
* Do not go above this order unless 0 objects fit into the slab or
* overridden on the command line.
@@ -576,12 +609,30 @@ static inline struct array_cache *cpu_cache_get(struct kmem_cache *cachep)
return cachep->array[smp_processor_id()];
}
+static size_t calculate_freelist_size(int nr_objs, size_t align)
+{
+ size_t freelist_size;
+
+ freelist_size = nr_objs * sizeof(freelist_idx_t);
+ if (IS_ENABLED(CONFIG_DEBUG_SLAB_LEAK))
+ freelist_size += nr_objs * sizeof(char);
+
+ if (align)
+ freelist_size = ALIGN(freelist_size, align);
+
+ return freelist_size;
+}
+
static int calculate_nr_objs(size_t slab_size, size_t buffer_size,
size_t idx_size, size_t align)
{
int nr_objs;
+ size_t remained_size;
size_t freelist_size;
+ int extra_space = 0;
+ if (IS_ENABLED(CONFIG_DEBUG_SLAB_LEAK))
+ extra_space = sizeof(char);
/*
* Ignore padding for the initial guess. The padding
* is at most @align-1 bytes, and @buffer_size is at
@@ -590,14 +641,15 @@ static int calculate_nr_objs(size_t slab_size, size_t buffer_size,
* into the memory allocation when taking the padding
* into account.
*/
- nr_objs = slab_size / (buffer_size + idx_size);
+ nr_objs = slab_size / (buffer_size + idx_size + extra_space);
/*
* This calculated number will be either the right
* amount, or one greater than what we want.
*/
- freelist_size = slab_size - nr_objs * buffer_size;
- if (freelist_size < ALIGN(nr_objs * idx_size, align))
+ remained_size = slab_size - nr_objs * buffer_size;
+ freelist_size = calculate_freelist_size(nr_objs, align);
+ if (remained_size < freelist_size)
nr_objs--;
return nr_objs;
@@ -635,7 +687,7 @@ static void cache_estimate(unsigned long gfporder, size_t buffer_size,
} else {
nr_objs = calculate_nr_objs(slab_size, buffer_size,
sizeof(freelist_idx_t), align);
- mgmt_size = ALIGN(nr_objs * sizeof(freelist_idx_t), align);
+ mgmt_size = calculate_freelist_size(nr_objs, align);
}
*num = nr_objs;
*left_over = slab_size - nr_objs*buffer_size - mgmt_size;
@@ -2032,13 +2084,16 @@ static size_t calculate_slab_order(struct kmem_cache *cachep,
break;
if (flags & CFLGS_OFF_SLAB) {
+ size_t freelist_size_per_obj = sizeof(freelist_idx_t);
/*
* Max number of objs-per-slab for caches which
* use off-slab slabs. Needed to avoid a possible
* looping condition in cache_grow().
*/
+ if (IS_ENABLED(CONFIG_DEBUG_SLAB_LEAK))
+ freelist_size_per_obj += sizeof(char);
offslab_limit = size;
- offslab_limit /= sizeof(freelist_idx_t);
+ offslab_limit /= freelist_size_per_obj;
if (num > offslab_limit)
break;
@@ -2285,8 +2340,7 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
if (!cachep->num)
return -E2BIG;
- freelist_size =
- ALIGN(cachep->num * sizeof(freelist_idx_t), cachep->align);
+ freelist_size = calculate_freelist_size(cachep->num, cachep->align);
/*
* If the slab has been placed off-slab, and we have enough space then
@@ -2299,7 +2353,7 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
if (flags & CFLGS_OFF_SLAB) {
/* really off slab. No need for manual alignment */
- freelist_size = cachep->num * sizeof(freelist_idx_t);
+ freelist_size = calculate_freelist_size(cachep->num, 0);
#ifdef CONFIG_PAGE_POISONING
/* If we're going to use the generic kernel_map_pages()
@@ -2625,6 +2679,7 @@ static void cache_init_objs(struct kmem_cache *cachep,
if (cachep->ctor)
cachep->ctor(objp);
#endif
+ set_obj_status(page, i, OBJECT_FREE);
set_free_obj(page, i, i);
}
}
@@ -2833,6 +2888,7 @@ static void *cache_free_debugcheck(struct kmem_cache *cachep, void *objp,
BUG_ON(objnr >= cachep->num);
BUG_ON(objp != index_to_obj(cachep, page, objnr));
+ set_obj_status(page, objnr, OBJECT_FREE);
if (cachep->flags & SLAB_POISON) {
#ifdef CONFIG_DEBUG_PAGEALLOC
if ((cachep->size % PAGE_SIZE)==0 && OFF_SLAB(cachep)) {
@@ -2966,6 +3022,8 @@ static inline void cache_alloc_debugcheck_before(struct kmem_cache *cachep,
static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
gfp_t flags, void *objp, unsigned long caller)
{
+ struct page *page;
+
if (!objp)
return objp;
if (cachep->flags & SLAB_POISON) {
@@ -2996,6 +3054,9 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
*dbg_redzone1(cachep, objp) = RED_ACTIVE;
*dbg_redzone2(cachep, objp) = RED_ACTIVE;
}
+
+ page = virt_to_head_page(objp);
+ set_obj_status(page, obj_to_index(cachep, page, objp), OBJECT_ACTIVE);
objp += obj_offset(cachep);
if (cachep->ctor && cachep->flags & SLAB_POISON)
cachep->ctor(objp);
@@ -4232,21 +4293,12 @@ static void handle_slab(unsigned long *n, struct kmem_cache *c,
struct page *page)
{
void *p;
- int i, j;
+ int i;
if (n[0] == n[1])
return;
for (i = 0, p = page->s_mem; i < c->num; i++, p += c->size) {
- bool active = true;
-
- for (j = page->active; j < c->num; j++) {
- /* Skip freed item */
- if (get_free_obj(page, j) == i) {
- active = false;
- break;
- }
- }
- if (!active)
+ if (get_obj_status(page, i) != OBJECT_ACTIVE)
continue;
if (!add_caller(n, (unsigned long)*dbg_userword(c, p)))