Commit 3acd4850 authored by Christophe Leroy's avatar Christophe Leroy Committed by David Sterba
Browse files

btrfs: fix allocation of free space cache v1 bitmap pages 



Various notifications of type "BUG kmalloc-4096 () : Redzone
overwritten" have been observed recently in various parts of the kernel.
After some time, it has been made a relation with the use of BTRFS
filesystem and with SLUB_DEBUG turned on.

[   22.809700] BUG kmalloc-4096 (Tainted: G        W        ): Redzone overwritten

[   22.810286] INFO: 0xbe1a5921-0xfbfc06cd. First byte 0x0 instead of 0xcc
[   22.810866] INFO: Allocated in __load_free_space_cache+0x588/0x780 [btrfs] age=22 cpu=0 pid=224
[   22.811193] 	__slab_alloc.constprop.26+0x44/0x70
[   22.811345] 	kmem_cache_alloc_trace+0xf0/0x2ec
[   22.811588] 	__load_free_space_cache+0x588/0x780 [btrfs]
[   22.811848] 	load_free_space_cache+0xf4/0x1b0 [btrfs]
[   22.812090] 	cache_block_group+0x1d0/0x3d0 [btrfs]
[   22.812321] 	find_free_extent+0x680/0x12a4 [btrfs]
[   22.812549] 	btrfs_reserve_extent+0xec/0x220 [btrfs]
[   22.812785] 	btrfs_alloc_tree_block+0x178/0x5f4 [btrfs]
[   22.813032] 	__btrfs_cow_block+0x150/0x5d4 [btrfs]
[   22.813262] 	btrfs_cow_block+0x194/0x298 [btrfs]
[   22.813484] 	commit_cowonly_roots+0x44/0x294 [btrfs]
[   22.813718] 	btrfs_commit_transaction+0x63c/0xc0c [btrfs]
[   22.813973] 	close_ctree+0xf8/0x2a4 [btrfs]
[   22.814107] 	generic_shutdown_super+0x80/0x110
[   22.814250] 	kill_anon_super+0x18/0x30
[   22.814437] 	btrfs_kill_super+0x18/0x90 [btrfs]
[   22.814590] INFO: Freed in proc_cgroup_show+0xc0/0x248 age=41 cpu=0 pid=83
[   22.814841] 	proc_cgroup_show+0xc0/0x248
[   22.814967] 	proc_single_show+0x54/0x98
[   22.815086] 	seq_read+0x278/0x45c
[   22.815190] 	__vfs_read+0x28/0x17c
[   22.815289] 	vfs_read+0xa8/0x14c
[   22.815381] 	ksys_read+0x50/0x94
[   22.815475] 	ret_from_syscall+0x0/0x38

Commit 69d24804 ("btrfs: use copy_page for copying pages instead of
memcpy") changed the way bitmap blocks are copied. But allthough bitmaps
have the size of a page, they were allocated with kzalloc().

Most of the time, kzalloc() allocates aligned blocks of memory, so
copy_page() can be used. But when some debug options like SLAB_DEBUG are
activated, kzalloc() may return unaligned pointer.

On powerpc, memcpy(), copy_page() and other copying functions use
'dcbz' instruction which provides an entire zeroed cacheline to avoid
memory read when the intention is to overwrite a full line. Functions
like memcpy() are writen to care about partial cachelines at the start
and end of the destination, but copy_page() assumes it gets pages. As
pages are naturally cache aligned, copy_page() doesn't care about
partial lines. This means that when copy_page() is called with a
misaligned pointer, a few leading bytes are zeroed.

To fix it, allocate bitmaps through kmem_cache instead of using kzalloc()
The cache pool is created with PAGE_SIZE alignment constraint.

Reported-by: default avatarErhard F. <erhard_f@mailbox.org>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204371


Fixes: 69d24804 ("btrfs: use copy_page for copying pages instead of memcpy")
Cc: stable@vger.kernel.org # 4.19+
Signed-off-by: default avatarChristophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
[ rename to btrfs_free_space_bitmap ]
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 62fdaa52

fs/btrfs/ctree.h

+1 −0
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ extern struct kmem_cache *btrfs_trans_handle_cachep; 
extern struct kmem_cache *btrfs_bit_radix_cachep;

extern struct kmem_cache *btrfs_path_cachep;

extern struct kmem_cache *btrfs_free_space_cachep;

extern struct kmem_cache *btrfs_free_space_bitmap_cachep;

struct btrfs_ordered_sum;

struct btrfs_ref;

fs/btrfs/free-space-cache.c

+13 −7
Original line number Diff line number Diff line
@@ -765,7 +765,8 @@ static int __load_free_space_cache(struct btrfs_root *root, struct inode *inode, 
		} else {

			ASSERT(num_bitmaps);

			num_bitmaps--;

			e->bitmap = kzalloc(PAGE_SIZE, GFP_NOFS);

			e->bitmap = kmem_cache_zalloc(

					btrfs_free_space_bitmap_cachep, GFP_NOFS);

			if (!e->bitmap) {

				kmem_cache_free(

					btrfs_free_space_cachep, e);
@@ -1882,7 +1883,7 @@ static void free_bitmap(struct btrfs_free_space_ctl *ctl, 
			struct btrfs_free_space *bitmap_info)

{

	unlink_free_space(ctl, bitmap_info);

	kfree(bitmap_info->bitmap);

	kmem_cache_free(btrfs_free_space_bitmap_cachep, bitmap_info->bitmap);

	kmem_cache_free(btrfs_free_space_cachep, bitmap_info);

	ctl->total_bitmaps--;

	ctl->op->recalc_thresholds(ctl);
@@ -2136,7 +2137,8 @@ static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl, 
		}



		/* allocate the bitmap */

		info->bitmap = kzalloc(PAGE_SIZE, GFP_NOFS);

		info->bitmap = kmem_cache_zalloc(btrfs_free_space_bitmap_cachep,

						 GFP_NOFS);

		spin_lock(&ctl->tree_lock);

		if (!info->bitmap) {

			ret = -ENOMEM;
@@ -2147,7 +2149,9 @@ static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl, 


out:

	if (info) {

		kfree(info->bitmap);

		if (info->bitmap)

			kmem_cache_free(btrfs_free_space_bitmap_cachep,

					info->bitmap);

		kmem_cache_free(btrfs_free_space_cachep, info);

	}
@@ -2811,7 +2815,8 @@ u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group, 
	if (entry->bytes == 0) {

		ctl->free_extents--;

		if (entry->bitmap) {

			kfree(entry->bitmap);

			kmem_cache_free(btrfs_free_space_bitmap_cachep,

					entry->bitmap);

			ctl->total_bitmaps--;

			ctl->op->recalc_thresholds(ctl);

		}
@@ -3615,7 +3620,7 @@ int test_add_free_space_entry(struct btrfs_block_group_cache *cache, 
	}



	if (!map) {

		map = kzalloc(PAGE_SIZE, GFP_NOFS);

		map = kmem_cache_zalloc(btrfs_free_space_bitmap_cachep, GFP_NOFS);

		if (!map) {

			kmem_cache_free(btrfs_free_space_cachep, info);

			return -ENOMEM;
@@ -3644,7 +3649,8 @@ int test_add_free_space_entry(struct btrfs_block_group_cache *cache, 


	if (info)

		kmem_cache_free(btrfs_free_space_cachep, info);

	kfree(map);

	if (map)

		kmem_cache_free(btrfs_free_space_bitmap_cachep, map);

	return 0;

}

fs/btrfs/inode.c

+8 −0
Original line number Diff line number Diff line
@@ -74,6 +74,7 @@ static struct kmem_cache *btrfs_inode_cachep; 
struct kmem_cache *btrfs_trans_handle_cachep;

struct kmem_cache *btrfs_path_cachep;

struct kmem_cache *btrfs_free_space_cachep;

struct kmem_cache *btrfs_free_space_bitmap_cachep;



static int btrfs_setsize(struct inode *inode, struct iattr *attr);

static int btrfs_truncate(struct inode *inode, bool skip_writeback);
@@ -9409,6 +9410,7 @@ void __cold btrfs_destroy_cachep(void) 
	kmem_cache_destroy(btrfs_trans_handle_cachep);

	kmem_cache_destroy(btrfs_path_cachep);

	kmem_cache_destroy(btrfs_free_space_cachep);

	kmem_cache_destroy(btrfs_free_space_bitmap_cachep);

}



int __init btrfs_init_cachep(void)
@@ -9438,6 +9440,12 @@ int __init btrfs_init_cachep(void) 
	if (!btrfs_free_space_cachep)

		goto fail;



	btrfs_free_space_bitmap_cachep = kmem_cache_create("btrfs_free_space_bitmap",

							PAGE_SIZE, PAGE_SIZE,

							SLAB_RED_ZONE, NULL);

	if (!btrfs_free_space_bitmap_cachep)

		goto fail;



	return 0;

fail:

	btrfs_destroy_cachep();