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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 69d2480456 ("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: Erhard F. <erhard_f@mailbox.org>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204371
Fixes: 69d2480456 ("btrfs: use copy_page for copying pages instead of memcpy")
Cc: stable@vger.kernel.org # 4.19+
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: David Sterba <dsterba@suse.com>
[ rename to btrfs_free_space_bitmap ]
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Christophe Leroy 2019-08-21 15:05:55 +00:00 committed by David Sterba
parent 62fdaa52a3
commit 3acd48507d
3 changed files with 22 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
fs/btrfs/ctree.h
View File

@ -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;

20
fs/btrfs/free-space-cache.c
View File

@ -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 @@ new_bitmap:
}
/* 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 @@ new_bitmap:
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 @@ out:
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 @@ again:
}
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 @@ again:
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;
}

8
fs/btrfs/inode.c
View File

@ -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();